Dear student,

First of all you must mention the counselling name that for which counselling you are talking about .
Now recently as the josaa counselling registration is going on, so I assume that you are asking about josaa first round counselling.

Actually in josaa counseling anyone who has given JEE mains exam can register. Even the non qualified students of JEE mains can also register in josaa counselling though they will not get any seat.
Now in josaa counselling after you have locked choices and when the first round starts, it means in the first round as per your choices and rank, you will be provided the colleges as per your preferred choice, if you lie within a particular range of cutoff ranks set by the participating institutes. And if you get a seat in first round, and, if you want, you can accept the seat and get your provisional admission. After that you don't have to attend all the remaining rounds and similarly the other rounds are also there like this.
The first round of josaa counselling will be held on 17th october 2020.

Check out the following link to know more information and different dates of josaa counseling :-
https://engineering.careers360.com/articles/josaa-counselling/amp