How to fly quadcopter in a square?

Hi everyone, I’m new to ArduPilot. I am trying to learn how to do an autonomous flight and fly it in a square. I’ve already gotten the drone (pixhawk 6c) to fly with a controller manned.

I searched video on YouTube and they’re way too complicated and doing some crazy flight plan, all I need is a square.

Can anyone refer me to the right document or video for me to follow step-by-step? Or if you could please just list the instructions down. Thank you very much!