Hello Ashutosh

Joint Seat Allocation Authority will be conducting the counselling of JoSAA 2019 for all qualified candidates. Registrations for the counselling will open tentatively in the second week of June 2019. 

Candidates will have to register online to participate in the counselling. 

National Testing Agency will be conducting the JEE Mains 2019 exam twice a year in January and April. 
You can go through the link below and check the detailed information about the Counselling- 

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

Good Luck!

Once the result of JEE advanced is declared which is most probably in the second Sunday of June after while the counselling begans within a week and you need to register for joint seat allocation and then you need to give preference to your course in corresponding colleges in based on rank in JEE main and advanced you will be allotted colleges