In the track settings on the left, you can change a track to "mask (multiply)". you can also set tracks to parent/child. Or if you desire to green screen, you can use the Chroma Keyer FX.
If this does answer your question, please provide more details on what you're trying to accomplish.
just trying to figure out the software, is it only done with a video or can you mask a pict. i changed it to a "mask (multiply) i still don't get the spray can to mask. also can you clean up old vhs tapes on this software, my neighbor just asked me. sorry to get off subject.
"also can you clean up old vhs tapes on this software..."
Provided you import your VHS tape as source (pass-through a camcorder, or some other means), then yes you could do some limited cleanup on the audio/video. Checkout the FX, and read through help, it may give you some ideas.