Go to Section Info.
Select the Section Info tool from the Tool Menu in your site.
Click Assign Students.
Select students from the class list.
Click one or more student names in the list of unassigned site participants on the left, and then use the single right arrow button to add the selected student(s) to the section list on the right.
Click Assign students.
When you have finished adding students to the list on the right, click the Assign students button.