what is the first stage of becoming a professional badminton player

Hi Yash!

Here are two sites that will tell you much about becoming a professional badminton player:

https://www.quora.com/How-do-I-become-a-professional-badminton-player-as-a-beginner

http://www.badminton-information.com/Pro-Badminton-Players-Interviews.html

A very important thing for you to consider is a backup career that you might want to study for in case you have a career ending injury. Talk to you school counselor and your favorite teachers to see what might be a good backup career for you to follow.

Send thank you notes to those who help you. Please keep me posted. I would like to follow your progress.