The example used:

Determine the empirical (simplest) formula for a compound that is 32.4 % Na, 22.5 % S and 45.1 % O.

To start the calculation, assume 100g of the compound.  Set up a table and make the calculations as follows:

element	mass /g	molar mass /g mol-1	moles*	ratio
Na	32.4	23.0	1.41	2.01
S	22.5	32.0	0.703	1
O	45.1	16.0	2.82	4.01

This gives the simplest formula of Na₂SO₄

*From the definition of molar mass:
n = m/M