How does ribbon dropping work?

If I understand correctly, ribbon dropping is when you enter a club, complete some HW tasks so that league ribbons will count toward the team, and then you leave. It is a nice gesture to teams who accept coffee jumpers (who drop in for coffee). It's not so accepting if the club was expecting a long-term teammate.

If you were a current member when teams were grouped for competition (before 3:00 UTC the day before the competition begins), you'll also be able to earn ribbons during the comp, and of course, get the team's reward when the comp ends.