What kinds of changes are you trying to make?
It seems that you are very new to After Effects. I recommend that you work your way through the getting-started materials here:
I couldn't paint or clone at first, but I was able to use the paint brush and clone tool by getting a new composition and then double clicking on it, but when rendering the AVI file back to AVI the changes flicker and the file looks very different, unnatural. Therefore, it is awful. Plus, I have movement so changes have to be made every frame to remove equipment so the program is useless, but thanks.
Here is a clip: www.specializedvideos.com/grant/chelseafix2.avi Download it and remove the equipment pole as I did and render the fixed file achieving the exact same quality as the original AVI file, as I couldn’t, and show me Adobe After Effects is useful.
Did you ever see a feature film with special effects? You've probably seen After Effects in action.
Read this article: http://www.adobe.com/motion/aviator.html
That's just one of many. I'm not going to do your work for you. Besides, your link is no good. I've been producing effects including removing unwanted items from a shot and replacing backgrounds with AE for 20 years. You can't learn AE in 5 minutes. You've got to practice.