How did competitors enter the arena? Well, that was a part of the test. They could try to walk up the wall, but to do that would require that they figure out the path, for not all the bricks in the wall would allow the Shinobi to grasp onto them with chakra.
They could try climbing it with there bare hands, but there were no grips. They could try many things really, but not many would work.
The Proctor: This man would explain everything above in much the same words. He would also tell the Genin that the rules of the actual fight would be explained once they reached the arena, and also that their opponent was already within.
Wall LayoutShow
Each colored square is one meter high by one meter wide. Certain squares will reject your chakra if you choose to try and walk up and if you step on such a square the entire wall will reject your chakra for a few seconds, long enough for you to fall and hit the ground. After you have hit the ground you can get up and try again, squares all back to how they normally are.