If you are signed in to the store, when you launch itunes you will get the store page. To get your music library you have to open settings, click on store (on the left), and then sign out. Then when you launch itunes you'll get your library.
Also, when I got my ipad I found that synching the music library was not enabled out of the box --- I had to select that manually.
Have fun.
--jrenwick22