How do you catch Pokemon in Pokemon colesseum?

Once you get the creepy girl to join you,she can see the black arora of the shadow pokemon.Then you go to the mart in Phnac City,Talk to all the people there,then one will evencully tell you the gur at the Outsrit Stand used to sell them,so go to the guy that owns the outskirt stand and he'll say so you want some pokeballs huh,then he gives you 5 free pokeballs.He also puts them on display so you can buy more.But the girl will only let you snag(catch)the shadow pokemon.