Hello,
You can connect to any account that you have the login info for and add it to track in QB as long as its a supported bank.
The IN QUICKBOOKS amount is the sum of ALL the transactions in the QB register for that account.
The BANK BALANCE is what QBO is showing your online bank account balance (this is the balance directly from your banks website)
Sometimes the 2 amounts will be the same but a lot of times it wont be and here is 1 big example why:
QBO won't download items until they fully post to your bank account. Depending on your bank (Chase is 1 example) the bank balance will include items that are still processing but haven't fully posted yet which also means they haven't been downloaded into QBO yet and so not in your register and therefore not part of the "In QuickBooks" balance.
If you're reconciling your account in QBO using the reconcile feature and reconciling against your bank statement...as long as it comes out even with no discrepancy, then don't worry about the 2 balances on the banking screen matching. Those numbers are always going to fluctuate and will do so quite often if you have a lot of transactions going in and out of the account.