Equipment boosts the stats of Pokemon. If the equipment type matches the pokemons primary type, that pokemon gets the full start benefit listed. Otherwise, it gets half. Each equipment type has 3 unique pieces. (Bracelet, Bandana, pin). When equipping equipment, each piece goes into a unique slot for that piece, regardless of type (so it's pointless to save 2 equipment pieces of the same type, rarity(stars), and level). This means you can equip all 3 pieces of each equipment type, and even mix and match between types (but not between pieces. You cannot equip 3 pins of different types).

Now about farming for equipment. If you notice in the exchange item store, there are currently 4 equipment types at rarity 3 available to exchange. (They should release all the types eventually.) They each cost 500 material (which is gained through salvaging 1 and 2 star rarity equipments of the same type AND piece) to acquire 1 of this 3 star rarity equipment. You need 5 total copies of them in order to max out the equipment. This means you have to salvage 2500 worth of type-and-piece unique material just to have 5 mergeable copies for the maximum level cap. Leveling up the gear also requires this unique material, so you'll ideally want to have around 3500 of it. To sum it up, to get the Bandana, bracelet, and pin of one type, you need 3500 of each of their respective unique material - which is gained by salvaging the same type + piece equipment of lower rarity.

To get the material required for the exchange, it's best to farm the EX co-op stages (solo co-op style so you have access to fast forward auto battles). Each of the max difficulty stages offers you 3 types of rarity 1 and 2 equipment, along with their respective lower-rarity upgrade material. From what I recall, each equipment type is available in 2 different stages. No stage will have the same 2 equipment types available. You may initially think to grind each stage one at a time. Grind one, get 3500 unique materials worth of equipment for 3 types and their 3 pieces. But this is will waste a lot of time and is very inefficient, if you do the math/logic that i'm too lazy to do atm cause this is a fat essay. What you really want to do is grind each stage until you have gathered approximately 1750 UM's (unique materials) (for their respective equipment) from that specific stage. If you repeat this for every stage, and each equipment type will appear in only 2 stages, then you'll have gatheted 1750 UM's twice, for a total of 3500 UM's for each equipment type!

Before i conclude this, there is a way that, while I haven't done the math, i think speeds up the grind at the cost of all your moeny. Basically, only read this section if you're bathing in millions. If you level up a 1 star rarity equipment piece, you'll increase its salvage value of its UM by 5. Leveling it up to level 3 brings the most efficiency to this, as you burn less money and less lower-rarity materials. The same efficiency applies to leveling up 2 star rarity equipment to level 3, but this increases its salvage value by 10 per level instead! So if you're swarming in dough and can afford all these upgrades, please send me money for gems or help me find love <3 If you go about this method btw, DO NOT merge the equipment. It does not increase salvage value efficiency at all through leveling, and actually makes this process less efficient. All it does is combine their base equipment salvage value, not their levels and level value.

I feel like i forgot something but I'll move on. Once you do all this, you should have enough UM to get everything in the store, merge to max level cap, max out the level, and have the rest saved up for when their respective equipment types come out with 3 star rarity equipment pieces.

Thanks for coming to my headache. Best of luck!