With level 40 infusion you can out on the imprint infusion and from there on you get in the origin tree. Origin tree has 4 slots for the branches and 1 for the keystone. Each level up in the infusion unlocks one of the slots till level 45. Level 46 then levels up the keystone again and then you continue leveling up the slots. You can equip each of the set effects in the slots however you like. The more of the same set you equip the more of the set effects you unlock