In general, college students compete in several different events at each tournament. Tournaments are set up so that students can usually do 4-6 events. Yes, actually there are several national tournaments you can attend. Tournaments run throughout the year, from September until late April. Usually tournaments are held on weekends.
Tournaments vary in length from one day to three days.
This is called a swing. The seasons run concurrently. Often, debate and speech events are held at the same tournament. Nothing, but your time. Since the MSU speech and debate is a student-funded activity, it is open to any MSU student.