The following demo is saved as BasicAnimation/demos/FrameByFrame.fla. Take a look at the timeline. You will notice two layers (named number and back) and a timeline which spans 50 frames. Note the keyframes on the number layer.
Drag the playhead from the beginning to end. This will give you a sense of how the movie will play. But, did you drag too fast or too slow? How fast will the movie play? The Properties Panel shows that this movie will play at 24 frames per second. That means it will last about 2 seconds.
If you press the Enter key (or Return on a Mac) you will see the timeline in action as Flash moves the playhead for you.
Hide the back layer and the blue box will disappear. Hide the number layer and the numbers will disappear.