After taking BITSAT, you are supposed to fill you preference form, it should reach BITS by 20th June.
In Iteration 1, if you are offered admission, you have to pay a certain amount to keep your seat. If you are waitlisted, you have to pay a certain amount to stay in the waiting list.
People who dont pay the required amount before due date are chucked out, and Iteration 2 happens. Some people from iteration 1 waiting list are offered admission. These people who are offered admission in iteration 2 have to pay some fees to keep their seat. People who are still waitlisted are advised to wait for Iteration 3 and 4 results.
This whole process repeats till Iteration 4 or 5... You don't need to visit the instt for counselling, everything is done from the comfort of your home. Just make sure you keep checking results every 4-5 days, and pay any fees that is required to be paid before the deadline.