Manual accounts are updated by you and not connected to any bank. This way, you can track anything... from valuables like jewelry, real estate, a bank account you can't sync, or to track cash-on-hand.
To add a manual account, select the account type and add any relevant information as in the picture below.
Now that you have a manual account, you can update the account total by either adjusting the balance or adding individual transactions.
Learn about adding manual transactions here!