You can track a loan and what you owe to that loan by creating a manual financial account. Call it "Loan" or whatever you'd like and mark it as a "credit account" (implying it's money owed.)
The starting balance should be the total of the loan and will be a negative amount, denoting that you OWE money.
Whenever you make payments to the loan, create a manual deposit transaction. If you are making payments from an account set up within LessAccounting (like your business checking), then create it as a transfer instead of just a deposit. At any time you will be able to see what you've paid and what you still owe.