OK, so you've created a library. Now let's look at managing it successfully.
Click the Libraries button and you'll see a menu showing:
My Books - access any books you've created (that aren't in a library).
Libraries - access any of the libraries you've created.
Shared with me - Any libraries you've joined.
Click the 3 dots on a library to access the menu options for that library. These are your options:
Invite - generate a code for the library. This code can be sent to students (or other teachers) to have them join your library. You can also Expire this code to stop new users joining the library.
Settings - from here, you can rename the library, and toggle whether or not users can access Google Image Search within that library, and whether students can see each other's books.
Rename - give the library a new title.
Archive - you can archive the library and make it inaccessible to anyone else but you. Read more about archiving your library.
Managing users in a library
Click the Authors button in the toolbar and you can filter which books you see in a library. You can view just your books, everyone's books, or books made by a specific person. From here, if you are the library owner, you can remove users from your library by clicking the 3 dots > Remove user.
Moving books to a library
If you've got books on your bookshelf that you want to move into a different library, it's straightforward. Click the Books icon beneath your book and then click Move to Library. You can then choose the library you want to move the book into.