For this hidden compartment, all you need is; a ring with ring case, and an object you are attempting to hide.
Step 1: Compartment
Pull bottom up using the ring slot.
Step 2: Find Compartment
Look at the bottom of insert, and find stuff to fit in it.
Step 3: Hide Objects Inside!
Step 4: Close It Up
For this last step, all you have to do is close the bottom of compartment. This makes whatever you hid inside completely invisible.