Although both the words refer to the female gender, there is a stark difference between the two. And that is the number of the noun.
While the noun woman is used to refer to the singular form, the word women refer to the plural form. In other words, ‘woman’ is singular, and ‘women’ is plural.
‘Woman’ is pronounced as woo-man, whereas ‘women’ is pronounced as wee-men.
Woman refers to one female individual.
Women refers to more than one female individual.