Chemical particles like atoms and molecules are counted using moles. A mole, also termed Avogadro's number, is 6.02 x 10^23 particles. It is probably the single most important unit of measurement in chemistry.
In order to calculate the number of grams per mole, or molar mass, of H2SO4 start by finding the atomic mass of each element in the substance. Atomic masses can be located on most periodic tables of elements and may vary slightly from table to table. Use the one in your textbook.
2 x H = 2 x 1.0079 = 2.0158
1 x S = 1 x 32.064 = 32.064
4 x O = 4 x 15.999 = 63.996
Therefore there are 98.076 grams in 1 mole of H2SO4.