The majority of English nouns form a plural form simply: you just need to add -s/-es to the end of a word. But also there is a wide range of exceptions that makes the main rule a bit more difficult. Some plurals are formed logically but some forms must be memorized.
Main rules
As we mentioned above, most of English nouns form its plural by adding -s/-es to the end of a word.
For example 👇
a dog 👉 dogs
a table 👉 tables
a door 👉 doors
If a singular noun ends in s, x, z, ch, sh, we add -es to make a plural form.
For example 👇
an actress 👉 actresses
a bus 👉 buses
a birch 👉 birches
a tax 👉 taxes
a bush 👉 bushes
Sometimes we need to double -s when a word ends in the same letter.
For example 👇
a gas 👉 gasses
If a word ends in -y and has a consonant before it, we make an -ies ending.
For example 👇
a city 👉 cities
a baby 👉 babies
a lady 👉 ladies
a fly 👉 flies
If a word ends in -y and has a vowel before it, we add -s.
a boy 👉 boys
a day 👉 days
a way 👉 ways
If a word ends in -o, we add -es to it.
tomato 👉 tomatoes
potato 👉 potatoes
But:
a photo 👉 photos
a piano 👉 pianos
Be careful, there is a big list of exceptions that needs to be memorized 👇