In Book Creator online, a teacher can create a library and invite students to join. Note, this feature is not available in Book Creator for iPad.

Each teacher starts off with 1 library that can accommodate 40 books (more libraries and books are available if you upgrade to a paid subscription).

Click on the Teacher Dashboard icon in the top toolbar (the 3 lines in the far left of the toolbar). This will bring up the Teacher Dashboard, like below.

Find the Create a new library button and click it. 

You'll need to give the new library a name, and you'll see the optional library settings.

When you're ready, click on the Create library button. All done!

Next, you'll want to know how to Invite others to join your library.