They used practice swords (dull, but could still seriously injure and possibly even kill), and wooden shields. They also trained against other Gladiators. I hope this helped :)
Gladiators were either slaves sold to Gladiator schools and trained, condemned criminals, or, very rarely, paid volunteers. Sometimes, even emperors were gladiators, willingly.
They were taken as prisoners from war or were strong slaves and forced to fight to their bloody death or until they won so much that they could buy or win there freedom.