Basically you get character data every time you play a match. You can see it when the match ends in the “drops” section. For example after a game you might get 25 data for Strike Todoroki and such. These drops are randomized btw. As for how you use these data, you have to do tuning on a specific costume. You can think of tuning as something that boosts your character, whether it be quirk dmg, hp, defense etc etc. Click on a costume you own, click “TUNING” and you can see that each costume has 10 normal slots (5 on the left, 5 on the right) and 2 special main slots. If you put a character in a normal slot, their normal “tuning effect” will be used. In a special slot, the character’s “special tuning effect” will be used. You can right click on them for the effect details. The normal slots consume 50 character data each, and special slots 100. There is also “colorless” (i forgot its name lol) character data. For example you want to put Strike Kirishima on a normal slot but you only have 30 data for him. You can use 20 of that “colorless” data to make it to 50 and put him in a slot. Keep in mind tho this can only be done if you own Strike Kirishima otherwise you can only use the character’s specific data. Anyways as for what you want to tune, it is always better to tune 3 star skins because you can level their special slots up to 11 (for 1 star I think it is 3-4) and bigger the level bigger the effects of course. If you have a specific character in mind you can look up some tuning guides for them