(edition 3.5)
I am fairly new to D&D and am not sure what all the terms mean
Changeling is a race in the Eberron Campaign Setting or in Races of Eberron. They're basically shapeshifters, masters of disguise, descendents of humans and doppelgangers. Notably, they can be played at level 1 (doppelgangers have 4 racial levels and a +4 level adjustment, so a doppelganger with no class levels is an 8th level character).
"Changeling Rogue" is a racial substitution level - a regular class level with altered abilities, only open to specific races - in Races of Eberron. Here, it exchanges Trapfinding for 2 extra skill points and Social Intuition, which (among other things) lets you take 10 on a bunch of social skills and speeds up how quickly you can use them. (Races of Eberron also has a few other changeling feats which lend themselves well to disguise and fooling others.)
Factotum is a class in Dungeonscape. It's basically a bit of everything, shifting its role around as needed. It can be a good backup warrior, a backup healer, a backup caster, a skill user, and so on, but it can't keep them all up for long. Generally speaking they're high on Intelligence and operate like a bit of a rogue; if you can't decide on feats, pick Font of Inspiration as often as you can.
For an example of how a changeling rogue can be this kind of character, see the Uncanny Trapsmith linked in my signature. It doesn't use factotum by default, but it easily could, and the original version of the build (the "Stage Crew Gnome" which would also work with changeling) makes good use of Factotum.
Changeling is an Eberron race that has some simplified doppelganger characteristics but can be played from first level. The may also be a Savage Species type progression for the doppelganger which basically take the race and breaks it down into an eight level "class" that you must take before getting levels in anything else.
Suffice it to say, new players should always stick to "LA+0" races (those with a level adjustment of 0), like all the core races, since they're by far the easiest races to play and learn the game. They also tend to be better in the long run - level adjustments eat into your hit points and stats. (In the above example, a Doppelganger Rogue 1 is an appropriate character to play alongside a party of 9th level characters... except the doppelganger only has 5 hit dice worth of HP, and has a lower attack bonus as well.)
Changeling stats in a nutshell look something like this (I can't post them all, for copyright reasons, but here's the nutshell):
-No ability score adjustments
-Medium size
-Small boosts on mental defenses due to slippery minds.
-Small boosts on deceptive and manipulative social skills
-Natural linguists, they always have Speak Language as a class skill
-Minor Change Shape, which is basically an at-will non-magical Disguise Self effect that only affects the changeling (not the clothing he or she wears).
-Favored class: Rogue.
Is that close enough to a doppelganger for you? They can't read minds by default, but it isn't hard to do that through equipment or by taking levels in Telepath. (A dorje (wand) of Read Thoughts with two uses per day (instead of 50 charges) is pretty cheap, and Use Magic Device will let you activate it.)
Once again, I have to bring up the Uncanny Trapsmith as an example of this kind of character.
i will probably just stick with a human rogue or something seems a lot easier to make. thanks for the help though i might try making one in the future when i am more experienced
Incidentally? Humans are also level adjustment +0.
Therefore, the only difference between making a human rogue and making a changeling rogue is what set of racial characteristics you write down.
If you choose Changeling: The list above.
If you choose Human: A bonus feat and four bonus skill points (plus an extra skill point each level).
That's it. You proceed identically from there!
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If you choose Changeling and have Races of Eberron, you have an option:
You can choose to take a level in "Changeling Rogue", in which case you get 10+Int base skill points and Social Intuition, and you pick one Knowledge skill to be a rogue class skill.
You can choose not to take that level, instead taking regular "Rogue", in which case you'd get 8+Int base skill points and Trapfinding.
In both cases you'd gain the rogue's weapon and armor proficiencies, base attack bonus, saving throw bonuses, d6 hit die, and Sneak Attack 1d6.
This only applies at level 1 (although there are separate substitution levels later on); any level that is NOT a substitution level is identical in all ways to a rogue level. (i.e. both of the above choices lead to the same level 2 rogue next level, gaining Evasion and a few other goodies.).
You can choose to take a level in "Changeling Rogue", in which case you get 10+Int base skill points and Social Intuition, and you pick one Knowledge skill to be a rogue class skill.
You can choose not to take that level, instead taking regular "Rogue", in which case you'd get 8+Int base skill points and Trapfinding.
In both cases you'd gain the rogue's weapon and armor proficiencies, base attack bonus, saving throw bonuses, d6 hit die, and Sneak Attack 1d6.
This only applies at level 1 (although there are separate substitution levels later on); any level that is NOT a substitution level is identical in all ways to a rogue level. (i.e. both of the above choices lead to the same level 2 rogue next level, gaining Evasion and a few other goodies.).
Are these boards policed that heavily that you can't be a bit more specific about the Changeling? Of course now I go and find my book and see the description is pretty accurate. To put things a little differently:
Changelings suffer from, or can benefit from, anything that specifically targets the shapechanger subtype just like a doppelgange would.
Changelings match the standard elven resistance to sleep and charm.
Their supernatural shapechange ability may be Disguise Self (without the illusion) but the mechanical benefit is basically a +10 on the Disguise Skill.
They also get a +2 bonus on a few other skills.
For what it's worth when I design character I rarely factor race into it at all unless it is an essential part of the build. Essential as in I must be that race to get something or avoid multiclassing penalties (yes, some of us will still enforce those) because I try to no over-optimze. You could build a "master of disguises" to work with any species it is just that some species will have it work better. While they can certainly be nice I rarely pay attention to many of the specialized "substitution" effects that may be available.