First, let's access your items. To do that, you simply need to tap your item slots on the main screen! You can also select your Character, tap on Stats, and then on "Items" on the left side of your screen.
Slots can be empty, meaning they're ready to receive a new item or with a lock icon in front of them, meaning that you still need to get them.
Your available items will be in the “Found” category. You simply have to click on the one you want and then on "Equip". You follow the same steps to replace an item, in this case, the only difference is that it will ask you to select which slot you want to place your new item, substituting the old one.
This is also the place where you can get more information about the item by tapping on “Info”.
You will also notice Items To Be Found. These are all the other cool items that you can unlock by opening Toolboxes! :)