The description is miss leading. You have to unlock the weapons and then play with them.
There are four of each in the game. they can be unlocked with different gems that are collected through the dungeon at a moderate pace, or you can use your hard earned money and buy gem packs.
That's the bad news.
The good news is you can simply load up a level, select a different item each time and quit out. Once you quit out with your forth item , this will unlock.