Most tournaments limit students to single entry in debate patterns and double or triple entry in individual events. You can set a variety of entry limits from the Setup->Events page:
From there, you will see an "Entry Limits" section on the left hand side. On that page you can set limits by pattern, by division, or by particular events:
If you have variations - such as open division events in pattern A can double enter by novice events can single enter - you'll want to set it as double entry for pattern A and then single entry for the novice division. That way the program will know that by default, pattern A can double enter. And then in novice, limit students to single entry.
Pattern Limit refers to how many entries in that pattern a student can enter. Most tournaments set this at double entry for individual event patterns and single entry for debate event patterns. If you have a pattern with both individual events with double entry and debate events with single entry, set it to the higher limit (double entry). Then under the event limits set the competitor entries limit to 1 for debate events.
School Limit refers to how many entries a school can have in a particular pattern. Usually this is set to no limit.
You can also set limits by particular events:
Competitor entries refers to how many entries a student can enter in a particular event. Usually that's only 1 entry although some tournaments allow students to enter two duos. You can allow that by changing duo to "2 entries."
School entries refers to how many entries a school can enter in a particular event. Some tournaments limit each school to no more than 3 entries in any particular event.
Total Entries refers to how many total entries are allowed in a particular event. Some tournaments allocate a certain number of rooms (such as 4) to a particular event. If the tournament is allowing 6 max students per room with 4 rooms, you'd want to set the total entry limit to 24. Once the total entries in that event reach 24 entries, the program won't allow any additional entries from any particular school.