Confused with Chemistry?

To find m all you have to do is add up the molecule's elements. So to find sodium chloride which is "NaCl" so add 23+35=58 because that is the mes of the elements on the periodic table. to the find hydrogen chloride which is "HCl" so just add 1+35=36. Its simple but I am actually taking chemistry now in school but I got expelled the other day so I guess im not taking it anymore.