All 3 arenas are PVP arenas. You should spawn in a box of Lapis Lazuli blocks, with 2 sets of buttons on 1 side of the box that perform functions when pressed. This set of buttons is where you input the number of people who will be fighting each other, while this set of buttons will teleport the players to the requested PVP arena. Or, if you want to go to the arenas by yourself, just press any of the second set of buttons.

I'd also like to point out 2 things:
1. First, pressing any of these buttons does absolutely nothing except display a notification, so all players who want to teleport to a given arena will still have to use these buttons to teleport 1 by 1, not as a group.
2. There is no way to get back to the Lapis Lazuli box after teleporting to it, so unless you have flight, you will need to break a hole in the wall somewhere to get out of the arenas and back into the box. Also, the "Little Sphere" arena has a roof, so noclip is needed to get out of there without damaging it.

The good news to all of this is that you are in creative mode with cheats enabled, so so if you are ever stuck somewhere or are unsure what to do, your are able to fly around and repair damage easily.

I cant fint the pvp arena please help me