Thank you for posting in our Community! It sounds like you would like to invite students to join your class. You should see this option under Manage Class > Edit Roster > Add Student. This article outlines the process:
Please note that if your school is importing data such as rosters, this option may not be available to you. It might be a good idea to confirm by reaching out to an administrator through Help > Contact Your Organization.
Please let us know if you have questions or if this is not quite what you are seeing.