Good day, joan14,
I'm here to help record the post dated cheque you've issued to a supplier.
You'll need to use the Cheque feature and make it payable to the supplier you owe the money. Then, enter the installment date and enter Accounts Payable in the Category field.
Let me walk you through the steps on how to accomplish this:
When you receive the bill from the supplier, enter it as usual. The Enter and pay bills page will guide you through the steps.
If you have a lot of cheques to write, it is easier to download transactions directly from the bank.
Let me know if there's anything else you need. I always have your back.
Thank you and stay safe!