The Add accounts from other institutions function lets you add up to 20 accounts from other financial institutions to your account summary. You will see any accounts you add on your Account Summary page. The balances of the added accounts are then included when calculating your Total or Net Balance.
When you add an account from another institution, enter the account name and balance and choose if it's an Asset or a Liability. You'll have to update this information if anything changes as it won't update on its own.