Hi Model Name,
Reading just the formulas will only confuse you further.
You should understand by reading the theory in full, else you would always have the confusion.
Knowing a formula is not important in any chapter for IIT JEE Preparation. You should mainly understand how a formula is derived at, what are the conditions under which the formula is applicable. If the conditions change how do you work out the problem..... These issues have to be addressed in case you'll have to solve problems of IIT JEE.
So please go through the workings and understand the concepts in great detail.
Regards,
Ashwin (IIT Madras).