Hello Harsh!

I assume you are talking about JEE Mains. Even if it is not, the procedure is same for any councelling of entrance exam.

1. Visit the official website of the authority which conducts exam and the councelling. For example, if you have given JEE mains exam then visit JoSSA official website.
2. Login into their website using your username and password. Remember that you must use the same login credentials that you used for registration.
3. Then search for registration for councelling and fill the application form. Give proper details and cross check once before submitting.
4. Then you have choose your preferred colleges and courses.
5. Submit your preferences.

Remember all these procedure must be completed before the scheduled last date. The result of seat allotment will be declared later. you will get notified through the registered mail id and contact number. Once you are get that you have to pay seat acceptance fee as  mentioned and submit your documents for verification. You will then get your admission letter which you must produce to the alloted college along with required documents.

You can refer to the article below:

https://engineering.careers360.com/articles/jee-main-counselling-seat-allotment