After Effects cs3 - how to select frame to start effect?

I’m using after effects for the first time for years. I have a simple question and I just can’t seem to figure out how to select which frame I want to start a transition effect to start and end on?

In CS5 you’d have to use keyframes…don’t know if that works on CS3.

~TehYoyo

TehYoyo is right. Here is some more information about keyframing your effects.