CSAB is a counselling organized by central seat allocation board which provides counselling on the leftover seats after the josaa counselling you have to register for csab counselling in order to participate in it and the fee for such registration is different for different types of candidates which you can see from the information brouchre of csab there are two rounds in this counselling after 1st round you will have the option to withdraw your seat but after 2nd round whichever seat you have got will be binding on you and you will have to take admission in that college if you  do not do so then your fee will not be refunded so this is the brief of csab counselling in full detail you can refer csab information brouchre