I am trying to make an animation for holding a gun, however, I want the legs to move and the arms to stay in their animation form. How can I do this?
This wiki tell you exactly what you need :) I recently had this problem but have since solved it thanks to this wiki page.
Scroll down to where it says exclusion.
http://wiki.roblox.com/index.php?title=Animations
Most of the time, I realized that when you just loaded up Animation Editor, the default keyframe would animate all limbs, you might want to remove that and make a new keyframe.
It should look something like this. http://prntscr.com/hniazx
That'll exclude so that your Right Leg and Left Leg won't be animated.
( i really haven't noticed that until someone mentioned it to me )