The molar mass of something is simply the mass of that something (from the periodic table) in grams. 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.
So, what would be the molar mass of water? Water, as we know, 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:
The molar mass of any compound can be calculated in the same way. For instance, the molar mass of ammonium phosphate, (NH4)3PO4, is:
Of course to make sense of this you need to understand what formulas mean.