Study the rules:

• Use ending -s for plural nouns.

Examples: cat - cats, pen - pens, dog - dogs.

• Use ending -es if a noun ends in -s, -ss, -x, -sh, -ch, -tch.

Examples: fox - foxes, bus - buses, dish - dishes.

• Some nouns have irregular plural form.

Remember plural forms of the following words:
man - men

woman - women

child - children

foot - feet

tooth - teeth

mouse - mice

Now try this exercise:

Study more rules and do more exercises: Basic English Grammar Plural Nouns - 2