Keyframes
Keyframes occur when you put something on the the timeline that has a specific position at a particular frame. Every time you need to change position or something needs to change at a certain frame, such as size, etc., you need a new keyframe with the object reset for that frame.
To Add a Keyframe
1. Select a point on the timeline and Select Modify>Timelines>Add Keyframe and a new keyframe will appear.