After you run through a drill session, mark it complete from the session's detail page — pick the date you completed it and, if you want, add a short note (how it went, what to work on next time). This creates a completion record you can look back on later.
If a session has multiple participants, each person marks their own completion separately. If you built the session as part of a coach's class or series, your coach can see who on the roster has completed it and who hasn't — completion tracking is visible to them, not just to you.
Available to all users, including students.