Singular means only one. Plural means more than one.
The basic rule is to add s to make a noun plural.
There are many irregular nouns that add es. There are several rules to remember when spelling plural nouns. The rules are based on the letters at the end of the word. They are easiest to remember in categories.
Add s to form the plural.
cat ⇒ cats truck ⇒ trucks book ⇒ books
Nouns that end in s, sh, x, ch, or z
Add es to form the plural.
It is too hard to pronounce the words without the e. Try it – buss, brushs, foxs... you sound like a snake.
bus ⇒ buses brush ⇒ brushes fox ⇒ foxes
Nouns ending in f or fe
Some nouns ending in fe and some nouns ending in f just add s. Some nouns that end in fe or f change the f or fe to v and add es.
Check a dictionary if you are unsure which rule a noun follows.