So I've been playing around with AE trying to learn things here and there. My question I have right now is:

Why is it when I use the pentool around a certain area, sometimes the film outside the newly isolated figure disappears, and sometimes it doesn't? What am I doing wrong half the time?

The pen tool is used to draw masks. Whatever is outside the completed path disappears, whats on the inside is visible

so i just need to duplicate the layer under it?

What are you trying to accomplish?

Jim

Dark clouds turning to a lightnight storm. I was thinking I should mask the one layer where I want to brighten it with flashes of light.

Try using an adjustment layer with levels, and put your mask on the adjustment layer where you want the effect to show up.

Make sure the feather the mask so it's not a hard edge.

Hope this helps,

Jim