Creating a Contact Group for your class(es) can be very beneficial. It makes it easier to email your students all at once and share documents to groups by typing in the group name rather than typing in every email address.
You can create class lists by going to Contacts, clicking New Group and following the steps, typing in each student to create the group. If you have multiple classes, this can be somewhat time consuming. There is a way to create contact groups using your Infinite Campus rosters. Its not for the faint of heart - there are a lot of steps - but Nick Gagnon used some of his Google Summer Camp time this week to create a detailed tutorial. You should be able to follow the picture steps in his tutorial to create class lists based on each course.
Those instructions can be found here. Thank Nick next time you see him!
Creating a Class List Using Infinite Campus Rosters