All this means is that the student is following another students bookshelf. When they log in, they will be able to view their friends bookshelves to see what books they have added.
The only other thing they can do is leave a pre-scripted message. There is no free-form text allowed. The only information displayed is the students username, no identifying or contact information, and they cannot contact their"Friends" other than with the pre-scripted messages in the drop-down.
The idea is that students are encouraged to read more, and they expand their reading more, when they are following students bookshelves and getting exposed to books that other students are reading.