Nouns may be singular, when they refer to one of a kind, or they may give the idea of plural use. Plural use names two or more things.
Singular nouns book car sapling
Plural nouns books cars saplings
There are, also, many different endings for plural forms of words. Different endings of words are part of the language structure that is known as inflection. Included are -s, -es and some other forms. Good dictionaries give the plural form of nouns as an inflective addition. There are examples of inflections that are also found for the tenses of verbs and for some kinds of adverbs and adjectives.
Most words add the letter ‘s’ to the base word, however.
table tables
bird birds
reptile reptiles