Should you wish to create a new class, click into Class Admin:

Then click Create A Class. 

Give the class a name and click Add Class:

You will now see your class view:

To add a teacher to the class click Add Teacher. Using the selector tool find the name of the teacher you wish to add to the class, click the checkbox next to their name and click Assign. 

To add students to the class, it is a similar process, click Add Student. Find the name of the student you wish to add to the class and click the checkbox. Once you are happy with your selection click Assign.