It is quite simple .
Under Settings - Chart of Accounts you would create a Balance Sheet Liability account called “Benefactor Loan” or any other suitable name.
Assuming that you have already set a Bank account under the Cash Accounts tab, then you would Receive Money when the benefactor advances you the funds and Spend Money when there are any re-payments,
Have you read any of the Guides, if not, then click on Guides below. They will explain the above in fuller detail.