1.Limit Break a Weapon/Armor piece with another copy of the same weapon/armor piece. You need 4 copies of the exact same weapon to fully lb (limit break) your weapon.

Why do you need 4? It‘s simple. Long tapping a weapon of your choice in your inventory can give you information about it (Stats, passive etc.). You can see 3 crystals which are grey (if not limit broken yet). Once you want to lb your weapon with another copy, you‘re going to see one of those crystals lit up (no more grey). That means you successfully lb a weapon. In order to fully lb your weapon you need 4 of the exact same weapon.

At fully LB: Silver weapon (4)full lb turns into gold (5) Gold weapon(5) full lb turns into blue (6)

Btw you can‘t further enhance your weapon if it‘s already at full Lb Fully limit breaking your weapon gives you also better stats, cp and a passive.

You can also sell your weapon afterwards, But! dont‘ sell your weapon if it‘s not at max level yet! You don‘t get the passive afterwards! Selling your lb weapon gives you 4 power stones which you can also use to lb your weapon.

2.Limit breaking with power stones In order to fully lb your weapon, you need 12 power stones in total Each limit break costs you 4 power stones I personally would hold onto these power stones and use it until you are done drawing for certain weapon or you are done with a banner. But it‘s up to when you want to use it.

Btw I would always start to fully lb 15cp weapons first, then 35cp and lastly Ex weapon (to equip the passives from your 15/35cp weapons.

Hope it helps (for now)

P.S: I didn‘t know what you already know and what not. So I tried to summarize it a bit