How to create (record) a loan to a friend or vendor?

Add your friend as a new vendor or supplier.
Add a new loan payable account with account class as "Short Term Debt".
Create a payment with using transaction type as "Make or payment" or "Pay Expense"
Select your friend name as the vendor
Select the loan payable account and enter the amount
A journal entry will be created which will credit the bank account and debit loan payable account.
Print the cheque and click Process
When you receive the money back, creating another new payment with all same information but negative amount instead.
The second payment transaction will offset the first transaction of the loan.