1. Set up the liability account first. From Settings, open the Chart of Accounts and click New. Set the Account Type to Liabilities, and choose Line of Credit as the Detail Type if your version of QuickBooks offers it; use Notes Payable if it doesn't.
2. Enter the opening balance if the line already has one. If you already owed money on it as of your QuickBooks start date, enter that balance as of that date so it doesn't distort this year's draws and payments.
3. Record a draw. When you pull money from the line, record a Bank Deposit into your checking account with the line-of-credit account as the source. This correctly increases both your cash and the liability at the same time.
4. Record a payment. Use Check or Expense, not Pay Down Credit Card, which is specifically for QuickBooks' Credit Card account type and isn't meant for a line of credit. Split the payment across two lines: part reducing the liability account (principal), and part going to an Interest Expense account if the payment includes interest.
5. Reconcile the account periodically. Match it against the lender's statement the same way you'd reconcile a bank or credit card account, so the balance in QuickBooks actually tracks what you owe.