This feature is applicable to users who are subscribed to:
1) Classroom Lite or Plus
2) Buncee for Schools & Districts
Please watch this video to learn how-to create student accounts:
Note for Buncee for Schools & Districts Users: Creating a class using the aforementioned steps will not create a new class in Google Classroom or Microsoft Office 365. See this article for more details about Roster Sync with Google Classroom and Microsoft Office 365.