Characters who are in guilds now have access to a shared bank between all guild members. These guild banks can be found at each factions banks and at the neutral banks, and can be accessed through the Guild Vault. The Guild Vault looks different for each city.

Setting Up Your Guild Bank
If you are a Guild Master, here is an easy to follow series of steps for setting up the guild bank to be used by all your members.
Firstly, buy a tab. Once you have bought the tab, the basic permissions and icons are set to a default value. Now you can customise your bank. Subsequent tabs are more expensive to purchase, just like your personal bank.

Right click on the purchased tab to open up a range of icons to choose from. Here you can rename the tab to something more useful. This Guild Master decides to set up her guild tab to hold recipes for the guild. Naming it 'Recipes' and choosing an icon, she can then decide who will have access.

Using the Guild Options tab, the Guild Master can set permissions for each rank, deciding whether they can view, withdraw or deposit items to the bank.

It is not possible for the Guild Master to delegate the management of the Guild Bank. The bank can only be managed by the current Guild Master.

Permissions
Each tab of the Guild Bank has seperate rules to allow guild members to do different actions depending on their rank within the guild. The actions allowed for each tab are shown at the top of the Guild Bank window. Guild Masters can set these permissions to one of the following: Full Access, Deposit Only, Withdraw Only, or Locked.

• Full Access - the guild member can view, withdraw and deposit items in the tab. For Guild Masters, all tabs are always set to Full Access.
• Deposit Only - the guild member can view and deposit items in the tab.
• Withdraw Only - the guild member can view and withdraw items from the tab.
• Locked - the guild member can view the items, but cannot withdraw or deposit items. The Guild Master can also restrict viewing of the tab.

The Guild Master can also set how much gold a guild member can withdraw each day, and whether guild members can view the Guild Bank log.

Repairing with Guild Funds
The Guild Master can allow guild members to use guild funds to pay for repairs. If this option is available, a new icon will be shown at repair merchants.
The Withdraw Gold option determines the maximum repair expense a guild member can incur when paying with guild money. The repair payment cannot be split between the Guild Bank and the guild member's own funds.

Things to Note:

• Money taken from the guild bank to repair counts against your total amount to withdraw each day. So if you use 10g to repair, and you are allowed to withdraw 20g each day, then you will only have 10g left.
• The money you are allowed to take out each day is dependant on the amount remaining in the guild bank. If your guild bank has only 50g, and your withdrawal limit is 100g, you can still only withdraw 50g.
• Players with access to the guild bank should be trustworthy as the responsibility for ensuring that items are not stolen rests with the Guild Master.
• Logs allow the members and Guild Master to see who has deposited and withdrawn items from the Guild Bank.

source: http://www.worldofwarcraft.com