How to make a separate page with GET processing?

Question

WordPress

Good morning!
I wrote my question-answer plugin with my tables in the database, now I ran into a problem, how to create a separate page for a specific question.
I want to do something like - site.com/faq?post=1,2,3 or site.com/faq.php?post=1,2,3 (the faq.php file will be in the folder with the plugin or in the topic)
I searched everything, I found that it can be done somehow through add_query_arg() , but I don’t fully understand how to do it.
How to make wp see this file and be able to access it?
Help:(