A video tutorial which shows you how to use redeem codes in Project Penelope version 1.3. With redeem codes you can get more ingame items like gear and slots.
How do I redeem a code
In the bottom right, when the inventory is opened, it shows the different pages. Goto a blank inventory page (possibly page 2 or three). Then press 'esc' and redeem the code by following the menu. You just need to enter the redeem code. When you redeem it when not having a blank page selected you might not fully get the reward.
You can find redeem codes in this topic