Global Tracks are pre-generated songs that are browsable, playable, and downloadable by all subscribers.
The Global Tracks section is a great place from where you can get inspiration, just listen, or create similar tracks. You can search and browse this section to find exactly what you are looking for without having to create a track yourself.
My Library holds all of the Global Tracks that you favorited or tracks you created and saved. This section is unique to you and can not be accessed by other users.