Attendance is taken per meeting from the club's calendar. Anyone who can manage the club (an administrator, staff, or the club's advisor) can record it.
Once saved, the meeting shows a summary such as "12 of 15 attended," along with who collected the attendance and when. Re-opening the meeting lets you adjust it later.
The member list is refreshed each time you open the window: students who have joined the club since the last time are added, and students who have left are dropped as long as no attendance was recorded for them. Because a meeting with attendance can't be deleted, that record is preserved even if the schedule later changes.