There are several rotations for a 6 person team. Depends on what you guys want to play. If you really don't know a lot about how to rotate players on a team, I would highly suggest you seek some help from a volleyball coach.
Unfortunately you ask these questions: How do you rotate with only 6 players? And, do you have 2 each of these players? Setters, hitters, and passers?
If you do not understand how the game is played and what the players are supposed to do, the tournament is going to be a total let down. I am not sure how far you want to go.
If your team does not know how to rotate, this is also a bad sign. You are entering a tournament with people on your team who may not understand the game? or may not know or have the skills to play the game? Why spend $150 on a tournament when you guys have no understanding of the game? I am not trying to be offensive, but the tournament DATES: Regionals- Great Falls: June 15 & 16, Billings: July 19 and Finals: July 20 in Billings...
That doesn't leave a lot of time to train and practice unless you guys go hard and practice daily. Learn the skills and build the instincts for the game. It is usually not something that can be done over night.
I've been to volleyball camp when I was younger (think 30+ years ago) and I thought I knew how to play before then, but going to a week long volleyball camp from 7am to 12pm daily for a week, was eye opening. And as a young player this was an opportunity that helped me tremendously. Perhaps I would suggest you guys go to a volleyball camp and learn the basics and get that going first.
But the choice is up to you and your team.
I would certainly try to practice and learn all I could if I were you.
Also you may want to make sure your team is aware of the volleyball rules that are updated. Big Sky refers to nfhs.org's site for the rules.