does anyone know how to put font behind lets say someone walking donw a street in AE. so the letters would be on a wall of a building and behind the guy. So they will be inbetween the guy and the building. how do you do this.????? can it be done in AE???
Thanks

That is compositing. What you do is create a mask where the
person is walking in front of the text (this will be an animated
mask since the person is moving). Then you have three tracks.
One for the moving footage on the background, one for the
text (in the middle) and then the moving footage again in the
forground which only shows the footage through your mask.

how do you do a animated mask. that sounds like it takes a long time.

That is usually the most difficult and time consuming indeed.
I can't explain you how to animate a mask. It has to do with
keyframing etc. Check the manual on that.