You can open storage from the menu on the left side of town screen or from the equipment/cards lists.
You can put cards and equipment into storage - you can have maximum 32 storage units.
An in-game purchase is required to be able to use storage.
Once purchased, it can be used permanently.
A total of 50 cards/items can be put into each storage unit.
Locked ones can be placed in storage while still being locked, and they will be still locked when taken out from storage.
However, equipment you’re currently equipped with, and cards you’re using in a set cannot be placed into storage – please remove them and try again.