I am very new to wordpress coding and would like some pointers and simple language to explain how I would create custom account endpoints that does specific functions. For example, I am using woocommerce and i want to overwrite the functions.php file to add custom endpoints that lets a user to view his/her invested ammount and manage it. I know how to do a simple function to add the endpoint name onto the account menu but I have no experience coding whatsoever in creating the functions after.

Is this so called a rest API? I do not fully understand what rest API is so I do not understand the link between endpoints and rest API, and cannot find a beginner website on guiding me through writing code for endpoint functions like the one I mentioned above for example. Any link for education or pointer is appreciated.