Gear grants you certain bonuses in battle. There is the main gear trait, and up to 3 sub-traits associated with a piece of gear. You can have 3 items of gear at one time… a head piece, a shirt, and shoes. You want to focus your main gear traits to things you want in battle…example, I prefer Swim Speed, Ink Saver, and Ink Recovery…of course this changes sometimes based on the modes. For instance if you are playing Ranked you may want a main piece of gear to be Quick Respawn or Quick Superjump. Every item of gear has a main trait.
The more expensive piece of gear (rare gear) have 3 sub-trait slots, while cheaper gear only has 1 slot available. When you wear this gear you will unlock the sub-traits randomly. Each piece of gear has a “brand name” associated with it. Without the guidebook’s help it’s tough to know which brand gives you the best chances to get random sub-traits you want. It’s all a big roll of the dice every time a sub-trait gets unlocked. Example, Firefin gear has a higher chance to get Ink Recovery sub-traits, but only like 5% greater chance over everything else. I wouldn’t focus on that too much in the beginning. What you will want to focus on is the main traits, and see what works best for you and what you want most. Sub-traits are not as powerful as main traits but, at least in Splatoon 1, you could get 3 of the same sub-trait on one piece of gear and it would about equal the bonus percentage of the main trait. There are diminishing returns so ideally, you would want to make the most of your gear and get 3 main traits you want most, then 3 other traits per item of gear, basically giving you 6 main traits…but it’s incredibly hard to get matching sub-traits since it’s all random.
Super Sea Snails will grant you extra slots on your gear. This is why Splatfests are important. You WANT all of your gear to have 3 slots. Start off with your best pieces of gear and unlock the slots with snails. You should also be able to purchase snails from Mulch (I forget his name…the sea urchin kid). At least in Splatoon 1 you could buy a single snail for 30k. That’s a lot of coin! Also, with sea snails, you can have Mulch re-roll your sub-traits if you don’t like what they are. Unfortunately all 3 slots are re-rolled at once. I can’t tell you how frustrating it was re-rolling in Splatoon 1. One time I think I spent 40 Snails just to get a triple sub-trait on one item of gear! OUCH!
Splatoon 2 has made it a little easier and allowed for “Scrubbing” of clothing with 3 unlocked slots, which grant you “ability chunks” you can then later apply to gear which seems like a good idea, albeit a very time consuming one. I haven’t been able to really indulge in this. You first need to unlock the 3 slots in order to scrub them…and from my understanding thus far from reading, you’d need to collect a set number of scrubbed sub-traits you want to then apply to the gear. Example…in order to apply Swim Speed to any item of gear you want, you might need to scrub about 10 (unsure of the #) sub-slots worth of Swim Speed on gear in general. To apply more than one Swim Speed to your gear (Example…I want a Ninja Squid shirt with 3 Swim Speeds on it to negate the penalty of Ninja Squid which slows your speed), I would need 10 Swim Speed chunks for the first slot, 20 for the second, and 30 for the third. Yikes! I think I may find re-rolling for a triple easier!
Anyway don’t let it boggle your mind too much, this is mostly for ranked A and up battles where you see players with ideal gear which takes a lot of time and patience to acquire. In the start, just focus on your 3 main traits. Then you can play around with subs as you’re able. You CAN have 2 main traits be the same and get a little bit better of a bonus in that trait, but again diminishing returns. I do see players with rollers for instance that like to apply as much Run Speed as possible, even having 3 main traits of it. They do go very fast but the diminishing returns don’t make it worth it when you could have another ability instead and be more well-rounded.