So That's How They Make Transition Packs...

Today I came across a tutorial by ECAbrams about using the repeater. It took me about two hours to play with it and actually make something of good use, but I really feel like I have a better understanding of it now. With a bit more practice, I should be able to manipulate the repeater to do quite a few handy tricks for transitions, logos, and anything else that pops up in my grey matter. The thing that makes the repeater so powerful is that it doesn't just allow you to repeat; it allows you to manipulate the scale, position, and rotation of these shapes AS THEY REPEAT...What does that really mean? It means that I can take a rectangle, turn it into a slim little bar, and then make its repeated duplicates fan across the screen and change their scale in the process (see it here). All in all, it finally made sense how animators can make all those superb transitions from scratch. There's still much more to learn like... How does the alpha channel play into this? When I bought a transition pack once, it said it came with an alpha channel so that the user could color the transitions any way they wanted to.  How do I add that?  Also, how do I do circles? I tried for 30 minutes and got stuck. I suppose each shape is a bit different to animate.