I guess u mean the "bank" or vault at selrock. To go selrock u have to speak with a robot u can find on estherian enclave as well as table mountain (maybe at other cities too but not sure) maybe u can also buy a portal scroll to salan (not sure)

Once on selrock there is a portal, im not sure how is called, i think its the vault. go to that portal.

There there are few chest, when used, some of the chest will transform your cash into "coins" (for example, 1 million gold got turned into a single item "1 million gold coin"

that "coin" is a item like any other, u can keepit on your inventory or even store it, so u can put it on the shared stash and pick it with any other character.

With that "coin" (im not sure if they are exactly coins, maybe they are scrolls) go to "the vault" on selrock again and use a chest with reverse fuction (withdraw 1 million gold) the "coin" will be used and deleted and in exchange u may get the gold back.

Thank you very much :) I thought that portal was some kind of dungeon heheh