The changes in an animation occur in frames (usually along a timeline). Changes are made in special frames called keyframes (in order to have changes occur between keyframes see: Tweening)
Tutorial
1. Open frame.fla from the tutorial images you downloaded (see: Download)
2. click on a keyframe for the blue box. Then select the box and move it to a different position. Rewind the animation and play it to see your brilliant changes. Try completely altering the animation of both boxes