Dear student,

Man is a singular noun and it means ONE MALE PERSON.
On the other hand MEN is plural form of MAN. And men denotes more than one MAN or more than one male person.

Now, similary WOMAN means - one female person, or singular noun meaning one female person.
So, WOMEN is plural form of woman, and women means more than one female person.

So, man and woman are singular noun ( denoting male person ) and MEN and WOMEN are plural noun ( denoting female person ).