How can i configure a free tier compute engine?
You are doing it right. The instance will show on the billing as charged for, but it's deducted from the monthly bill if you did everything correctly. Just create the instance and check if Subtotal stays 0.00. The rest of the billing is irrelevant to you if you do not have any other resources.
To view the page I screencapped go to "View Detailed Charges" from the Dashboard of your project.
The link you shared has all the info you need to create the instance with the free "specs".