Before first use, the inserts should be placed on a baking tray and put in an oven on 180c for 4-5 minutes to dry out any moisture.
Once cooled (about 1min), the inserts should be placed straight inside the waterproof housing - down the sides of the camera, and sealed. The less time they spend in the open air, the more effective you will find them.
You can then use your inserts 4-5 times before needing to start the process again by drying them out in the oven.