Drawing and tweening via ActionScript?

Hi everybody,

I found out how to make for example a rectangle via the LineTo method. But how can I change the size of this rectangle and SEE it changing (ie a tween), not jumping from one format to the other?
I guess it has to do with using “elapsing time” in the actionscript? I find it hard to get info on this subject. Though it seems important because otherwise it is impossible to create animations.
Can anybody help with this?

Thanx!
Frank

PS I really like this site a lot. It is probably the best I know!