Using Special items

I have reached the ranking of 2nd Dan an dhave noticed a lot of treasure chests on the bottom after matches. I am pretty sure that they mean that I have unlocked something, but how do I use them? I see no options and it seems that they are utterly useless.

 

Go to the place on the main menu where to make a new character file, then go to edit file....this will let u change customs, be given advice, and use items.