In order to enter the tournament you need to earn a minimum of 100 Chips (for more info on these please check the Resource section of this FAQ). The more raids you do (and the more stars you earn through successful raids) the higher you will rank in the tournament.
Each tournament lasts 3 days 5 hours and 30 minutes, and there is a pause between tournaments lasting 30 minutes.
Get to the top of the tournament to win coins and other resources.