To calculate it.1st you need to know the heat of neutralization when one mole of H+ ions react with OH- ions.2nd you need to know the molar conc. to find out how much will react with how much.3rd Sometimes you are given the normality then you have to work with the Equivalent weights ratio to molecular weights ratio to find the molarity.
Read your book and follow these steps if you dont get the answer give the data of your problem.