you can use those items only to upgrade the items you've won with the slot machines. by doing so, go onto a slot machine, tap in the top left corner, and tap collection. then you can click on the items that can be upgraded. (i think it's only for the ones in the 3x3 box.) but you need to have a certain amount to upgrade them.
press down on a user to un-pin or delete users. it'll say smth like if you want to un-pin them.