in the hub, some pokemon are up for a fight.
start with the Poochyena on the right of the map.
talk to her and (if she has nothing to say) you'll see 'Let's go! (Lv. 1-4)'.
pick that and you'll go to a dungeon. fight your way to the top (5 floors) and fight the Poochyena (i have to win).
once you win, talk to her, then you can have fun with her or go home.