Hello fellow D&D Players. I am brand new to D&D and am about to buy the Players Handbook. I want to ask a few questions, and since I know nothing about this game, I was hoping to get enlightened to a few questions.
1. Can I make a Warlock Necromancer?
2. Can I pact with Death?
3. Would this character be able to travel with other companions?
4. Would the Wizard or Warlock be better suited to be a Necromancer?
Thank you for putting answers to my noob questions, and I hope to be playing soon. 
It's been a while since I read the relevant sections, but I believe the pacts available to warlocks in the PHB are Fiend, Fey, and Far Realm. I don't know that they have many necromantic spells. Wizards have a necromancy school, and there is a death cleric, so those might be better options for a necromancer.
The answer to your first question is, probably not. Warlocks possess very few spells that actually raise the dead or reanimate corpses. Your second question is answered with another no, at least, not without the aid of a DM helping you to do so. Your third question is yes. D&D is, more times than not, a cooperative game where a party of players and a Dungeon Master get together and make a story. The DM runs the campaign world and the events in it, and the players interact with that world and act within the events of it. And finally, Wizards are better suited to being a Necromancer than Warlocks. As far as I can tell, Warlocks only gain one spell capable of actually raising or reanimating the dead, and the spell, named Finger of Death has to kill the target first. Meanwhile, wizards recieve a host of Necromancy Spells, and also possess what's called "Arcane Traditions" which allow them to specialize in a particular form of magic. Necromancers gain a life-stealing effect, the ability to raise more undead than any other caster, and the ability to raise stronger undead.
Wow, Thank you Kahless, drizzt_zylo, and transcendantviewer for the info. This will help me delve into D&D a lot more easily. 
Do any of you have experience playing a necromancer or being in a game with one? My intent is not to be a ahole, it is to play the most OP way I know how in this amazing game.
I have a very low-level (3) necromancy wizard in Pathfinder, but that's very different than 5e. Gernerally speaking, you're going to be playing Chaotic Neutral, Lawful Neutral, possibly Lawful Evil, as messing with dead people is not considered Good. This, I think, is why people are warning you about not being the a-hole. You often need special permission from the DM to be evil anything (though in Adventure League LE is an allowable option). Just be s ure you can play well with others and be aware that paladins, clerics, etc. might not like you much. Also, if you have clerics and they pop Turn Undead, your minions might get hosed.
It's possible to play a necromancer without using those troubling Undead spells. Not sure about 5e, but there were plenty of good necromancy spells that didn't raise anything, but massively debuff enemies or give you temp hit points or something. Someone more familiar with wizards in 5e might have more advice.
Also, note that in places such as Adventure League, Death Clerics are illegal without a special certificate.
From a mechanical perspective...
Look at the different classes and find the mechanical abilities and benefits that best fit your idea of the character, rather than limiting yourself to the name of a class or their "official" flavor.
Classes are simply a job description - a skillset that mechanically defines your most common/most efficient/preferred approach to dealing with the other in-game elements (i.e., the world around you). Class only strictly defines the mechanical how and sometimes the mechanical what. It strongly influences the narrative how and what but doen't actually control them, and has very little to do with the why or who unless you choose to have it do so.
As mentioned, wizards get the widest variety of necromancy spells that do different things, and get basically all the spells that reanimate or summon undead. There's also an actual Necromancer class feature. Wizard will also give a wider variety of non-Necro spells that you can acquire to round out your repertoire.
A death cleric is harder to pull off if you're going to be playing in an organized public game at a store or someplace, but would work just fine in a home game as long as the character fits the tone of the campaign. Although they may not get some of the wizard's spells or the actual Necromancy school class feature, they do get the cleric's Domain abilities and can, with DM approval, choose Death as their domain. They also have access to the non-necromantic healing spells, which plays into the whole controlling life and death thing.
From a flavor/narrative perspective...
Almost any class with any sort of magic or even vaguely magic-flavored abilities can be flavored as a necromancer - even a monk using their "ki" abilities is manipulating their own life-force or that of others, and a barbarian could be channeling the spirits of the dead (his warrior ancestors, spirits of those he's slain, etc.) to power his abilities. In many cultures (real-life Ancient Egypt, for example), "necromancers" would be respected public servants tasked with caring for the corpses of the recently-deceased and guiding them along their way to the afterlife, and/or communing with the spirits of the dead for divination purposes or to beseech them for their favor/to watch over the community/etc...
Also, nearly anything can be reflavored to be powered by "pacts" with powerful beings that give you those abilities without actually being a warlock.
On a more general note, nothing anywhere states that a necromancer needs to be at all dark, creepy or evil. (I once had a necromancer who was a sweet, happy-go-lucky young whose family trade just happened to be necromancy, and the family largely used it to keep the dead things staying dead, move restless spirits on to the next world and put the undead out of everyone's misery.)
And it's also basically considered a written rule (despite not actually being actually written down) that characters shouldn't go around being anti-social wankers to everyone and especially not their party members.
As long as you're not doing stuff like walking around covered in skull designs or bits of bones, digging up random bodies or killing random people to get bodies to reanimate, etc., most party members and the general populace aren't going to have a problem with you as long as you're not going out of your way to play up the potentially darker aspects of it - particularly if you stick to only reanimating things the party has just killed.
So you wanna have command over the dead, eh?
Couple ways to do it. Really, four.
1. Oathbreaker Paladin. In previous editions they were called Blackguards or Antipaladins. They are unholy knights that command undead. Almost, though not always, not 'Good' characters.
2. Death Domain Cleric. They can be good or evil, as Death itself is a natural part of life and not necessarily evil. Plays as a mix between melee and magic user.
Both of those options above are not legal for Adventurer's League Organized Play. But if you're playing a home game, no worries, just ask your DM if it's cool.
3. Necromancer Wizard. You're a Wizard specializing in the Necromancy school. Nothing prevents you from using spells from other schools, but you get bonuses relating to Necromancy spells.
4. Warlock. And this is actually a bit of a stretch. With a Fiend patron, your powers are more related to Demons or Devils, not necessarily Undead (It's a very important distinction in D&D).
RaistlinZifnab wrote:
Great information to digest and ponder over.
Ah ha, thank you for the insight jaappleton. I now understand the distinction between Warlocks and Wizards.
I have 4 options before me then, Death Domain Cleric, Necromancer Wizard, Oathbreaker Paladin and Warlock.
Kahless, thank you for your help.
I will be sure to be polite and respectful to others, until they are not polite and respectful to me. 
Mad_Jack, I will try my hardest to fit into the story of my party, but I also would want to use my character to its full potential, so I would not be necessarily a "Good Guy".
Thank you all for the help. I am now on to studying these classes.
One last thing... Are the Death Domain Cleric, Necromancer Wizard, Oathbreaker Paladin, and Warlock all in the Players Handbook?
Tempest_Stormwind...that is so helpful. Thank you very much for the breakdown and helpfull way to help me understand the mechanics of the game.
RaistlinZifnab wrote:
You could also be a College of Lore Bard and when you get the ability to choose spells from any shcool of magic, you can choose your Necromancy spells that way.
Though, it's a bit slower, your Bard could sing songs of death and impending doom as well as tell of tales of when the dead roam the earth.
Slit518 wrote:
I don't want to be a bother, but would Chaotic Evil work with a Necromancer Wizard? Is there even such a title as chaotic evil?
Please keep in mind I am not trying to "doom" my character, I just am curious about options.
Chaotic Evil is one of the possible alignments in the game. But lots of people tend to frown on playing a chaotic evil character in a party of others who aren't necessarily evil, as it takes a fairly mature roleplayer to do so in a fashion that won't cause friction with the rest of the group.
Warlock 5, Wizard (Necromancy) 15 can make a lot of skeletons, plus control some other big nasty (like a Mummy Lord or Death Tyrant) with the level 14 feature that can make even more skeletons. Just use Feeblemind on the big nasty first.
Also, chaotic evil is not allowed in Adventure League play (only Lawful Evil, and only in specific factions). Playing evil characters will often cause table and party friction (unless everyone else is evil as well).
jaappleton wrote:
RaistlinZifnab wrote: