With Spinnup you can release singles, EPs or albums. A single can be 1-2 tracks, an EP 3-6 tracks and an album 7-25 tracks. When you pay for your release that means you are using that allowance of tracks at once.
For example, when you pay for a single release that doesn't mean you release 1 track now and 1 track later, it simply means you can have a single or double track single release at that time.