Dear student,

Josaa - joint seat allocation authority, is responsible for giving admission in nits, iiits, iits, gftis etc by online counselling.
Anyone who has given jee mains can participate in josaa counseling. And if you got alloted any seat in josaa counseling, then you can easily accept the seat by uploading the documents and giving the seat acceptance fees of Rs. 35000 (if you are general or obc candidate).

Now coming into csab or jee mains special round counseling.
Csab - central seat allocation board is responsible for filling the vacant seats in nits, iiits or gftis after the josaa all rounds counseling is over.
For participating in csab round you must have to give a participation fees of Rs. 36500 (for general or obc candidates). And this is the buddh difference between josaa and csab counselling. After of you accept the seat in csab counseling then again you have to pay fees of Rs. 35000.

Also check out the following link to know more about josaa 2020 counselling :-
https://engineering.careers360.com/articles/josaa-counselling/amp

Also check out the following link to know more about csab 2020 counselling :-
https://engineering.careers360.com/articles/csab-special-round-for-nits-iiits-and-gftis