In Book Creator for Chrome, a teacher can create a library and invite students to join.
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).
Creating your first library
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 options for whether or not you want to allow students to access the Google Image Search within Book Creator, whether or not students will be able to read each other's books, and whether or not student's can publish their own books.
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.