I was just wondering what formula most games use for determining the damage a bullet does. I guess I'm not sure how distance factors in.

I suppose most games depend more on where the bullet hits, ie in 1st person shooters, a headshot is worth more than a shot to the leg, and that could consist of a bunch of bounding boxes for example, which each return a different damage value when hit with a bullet, maybe based on the maximum damage dealable by the type of ammunition you're shooting.

Although i'm a beginner too.. thats one simple way you could do it.

If you want the real thing you might want to look at
http://en.wikipedia.org/wiki/Physics_of_firearms
http://en.wikipedia.org/wiki/Ballistics

And some others site about it, it's easy to find. Still in a game you might not want it to be 100% realist cause players don't like it when bullets drop due to gravity and don't end up in their crosshair :)

For a more gaming way, you could have settings for each type of weapon like
Standing/Walking/Running base accuracy
Accuracy lost per bullet/Accuracy gain by not firing
Starting force
Force lost per meter traveled
Hit location percentage (head = 100%, arms legs = 50%, chest 75%) of remainning force when hit or something like that.