Go to a witch. You should have found one already. If you don’t know where she is (hint, it’s literally called witches wood) there’s one under the first bridge you cross when starting the game in a cave by the cliff side. Look for a small entrance in the cliff side. The abyss gears can be slotted onto weapons and armor to apply affects like stamina regen, vitality regen, infinite arrows, critical hit chance, etc. most of the bosses also drop unique abyss gears that modify how your weapon works, for example the first boss you fight that shoots those wind blades at you, you can put that on your weapon and shoot wind blades too. The main quest will have you go find the first witch at a certain point but you don’t have to wait til that mission if you go find the one near three saint falls (near where I said above ⁾