Progressing Through Parallettes One
Parallettes 1 is designed so that you work through each Phase of Level A until it's completed. After that, if you want to go through the program again, you can do Level B. Level B is more advanced, and so it helps to have done Level A beforehand.
If you're unsure of where to start, try two weeks of Level A and if it's too easy you can go straight to Level B.