Now that you have your button constructed, you must get it to the main movie stage.
Click the small link at the bottom of the timeline called Scene 1.
When you click this link, It will send you back to the main stage and if you've done it right, your button will be there. Now, If you'd like to test to see if the button works so far, Go to Control>Test Movie.
This will simply show your button, but if you've done it right, it should react by getting larger (or smaller, depending on how you modified it in the OVER frame) when you roll your mouse over it.