Next in the sign up process is the "Manage Songs" link. Click on this now to start adding songs.
If you want to add songs later click "Skip for now" and come back to your profile page later.
When you are ready to add songs to your MySpace Music site go to your profile management page by clicking the "Home" link at the top of any MySpace page. Then click "Edit Profile". You will see a tab that says "Manage Songs". Click on this link to start adding your songs to your MySpace music site.