Can anyone explain what's going on with the slope video in the Breakout series(https://www.youtube.com/watch?v=YQzwVDMIfyU&list=PLea8cjCua_P0qjjiG8G5FBgqwpqMU7rBk).

I really didn't get the video at all and things weren't fully explained and I'd really like to know how it works before I move on :/