The Shrine of Secrets contains 4 random teachable perks which can be purchased and made available on another killer's Bloodweb. Should these perks be owned already, your shards will be exchanged for an amount of Bloodpoints instead. The Shrine will notify you if you already own a certain perk.
Shards are owned by spending time in your trials - you can earn up to 10 in a single game.
The Shrine will update once a week and will bring another random set of perks for you to choose from.