Normally, players can battle in the Arena 5 times for free each day.  If you want to continue to challenge opponents, you will have to use Arena Passes.  VIP3 players can buy one pass per day, VIP4 players can buy two passes, VIP 5 players can buy three passes, etc.

P.S. You will still have to spend crystals to immediately reset the Arena cooldown time and buy Arena passes.