Head to the desk that has a red mat under it located on the rightside area. Here you can pay your mortgage; access your account; and mail and save letters.
Pay Mortgage
This is how you can pay your mortgage to Tom Nook. Once the mortgage has been paid in full, your character will celebrate personally. After all the payments for the final expansion of your house are paid off, this option finally disappears.
Mail a Letter
Any letter you wrote on your co-villagers' stationaries can be mailed through these option. Usually Pete delivers the letters to your mailbox at 9AM. You can also read previous mails here. For sending a present, attach the gift to the letter first before you send out the mail.
Access Account
This option lets you create and check your bank account. Once you have reached the 99999 limit of bells, the excess money will be held inside money bags that you can carry normally as regular items. Having a bank account saves you the trouble of carrying money bags around and not only will it allow you to get special rewards, it helps you purchase special expensive items as well. Additionally, your account gains interest at a rate of 0.5% per month.
Total Bank Account: 1000000
Special Gift: Box of Tissues
Total Bank Account: 10000000
Special Gift: Piggy Bank
Total Bank Account: 100000000
Special Gift: Pelly's Pic
Total Bank Account: 500,000,000
Special Gift: Phyllis's Pic
Total Bank Account: 999999999
Special Gift: Town Hall Model
Save a Letter
This will be your choice to save mails and keep them. Basically an extra storage space, it holds up to 75 mails which can be attached with files as well, so it can double-up as an extra item storage area.