How do I create a sign up sheet for a class?
That depends on what you mean by "sign-up sheet". If you want students to pick specific time slots, Scheduler may do the trick, assuming your school has this tool enabled in Canvas. Please see:
How do I add a Scheduler appointment group in a course calendar?
How do I view or edit a Scheduler appointment group in a course calendar?
How do I remove students from a Scheduler appointment in a course calendar?
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