Alright, thats something I kept meaning to research, and since you asked, I figured Id go find out and help both of us.
Okay, heres what you do:
Click on the Track Motion Button, and you have a little timeline at the bottom, and all the dimonds. The dimonds are your keyframe controls. and what you want to do, in laymans terms, is called keyframing (or thats what Ive always refered to it as) set a keyframe at the frame you want your animation to start, by clicking the dimond witht the "+" then go to where you want it to end, and click that button again, now on the keyframe you just made change your position. Now, if you want it to just cut to a change, you can do that with keyframes if you want to, but I would recommend you just split the clip at where you want to change.
hope I helped