I signed up for both my personal account and then the free upgrade for teachers. As I was going through this process, I learned that you may want to do this in a meaningful way. You may want to create an account for yourself, that you don't mind putting out to the public. You may want to create an account that is your teacher account, with a different username, that you will share with your students. You may want to keep your personal bookmarks private from your students and the teacher account will give the students access into that account. That is just something to think about. Users do have the ability to keep collected information private.
Once you have gone through the process of creating the teacher account, you will have access to a teacher console in diigo. That is where you will be able to create groups of students that will be able to share links and information. You will be able to create specific logins for students - using an e-mail address or just a name. This is quite nice for younger students that don't have e-mail accounts, yet. You can also import that information using a spreadsheet - if you have a large class.
I believe diigo will allow teachers and students to work electronically, see each others research, and analyze the sources, without having to print out large amounts of material. It will also aid in the citing of sources, as we teach students to document their research. Diigo will be an online tool that I try to work with and share a lot this fall, when I get back to school.