After Effects Using stock footage for transitions

[ReneeMontoya]

I've recently purchased stock footage for After Effects, and being fairly new to the program, I'm not sure how I would use stock footage for transitions.

What I want to do is something similar to this:

http://www.aihouqi.com/motion-graph...clouds-smoke-in-water-mask-matte-1276768.html

I want to modify the stock footage to it reveals something underneath. How would I go about doing this? Would I have to use masking, or a certain blend mode?

I'm trying to explain this as best as I can.

Any responses to this would be greatly appreciated.

 

[costisefu]

wow. cool transition, just don't know if it would work on a wedding video.
I will follow this subject, maybe someone has a good advice.