Molar Mass

The molar mass of an element is simply the mass of that element (from the periodic table) in grams/mol. 

Thus the molar mass of carbon is 12.011 g/mol, the molar mass of hydrogen is 1.00794 g/mol and the molar mass of oxygen is 15.9994 g/mol.

Compounds also have molar masses. For example, we know that water has the formula H₂O, meaning that it contains two atoms of hydrogen and one atom of oxygen. A mole of water would then contain two moles of hydrogen atoms and one mole of oxygen atoms. The molar mass would then be:

2(1.01 g/mol) + 1(16.00g/mol) = 18.02 g/mol

The molar mass of any compound can be calculated in the same way. For instance, the molar mass of ammonium phosphate, (NH₄)₃PO₄, is:

3 { 14.01 g/mol + 4(1.01 g/mol) } + 30.97 g/mol + 4(16.00 g/mol) =149.12 g/mol

Of course to make sense of this you need to understand what formulas mean.