Are there any explanations on how to play those Casino Guru tournaments? On what casino?

Hello, I would start with the very description you may find on the appropriate site:

"Free Slots Tournaments

Compete against other casino players in free slots tournaments for a chance to win valuable prizes. 100% free, no real money needed to play."

Just click and play the free tournament.

http://www.kpvfaw.com/tournaments ??

"About our tournaments

On this page, you can find our ongoing free slots tournaments. You can join any of them absolutely for free and win valuable prizes if you make it to the top of the leaderboard. To join, log in to your Casino Guru account or sign up if you haven’t already.

Over the duration of each tournament, you can play up to 100 spins per day. Points are earned by hitting winning combinations in included slots. The player who earns the most points altogether wins the tournament. Good luck!"