The suffix -s (or -es) is added to the end of words to show there's more than one of something. One cat becomes two cats. One box becomes several boxes. One story becomes many stories.

This tiny addition is one of the most important tools in English. Without it, we'd have trouble distinguishing between “I ate one cookie” and “I ate seven cookies,” which matters quite a bit when someone's counting what's left in the jar.

The suffix works for most nouns: dogs, trees, pencils, computers. When a word ends in certain letters like s, x, z, ch, or sh, we add -es instead: buses, foxes, lunches, wishes. Words ending in y often change to -ies: babies, butterflies, cities.

Some words refuse to follow the pattern. One child becomes multiple children, not “childs.” One mouse becomes several mice. These irregular plurals keep English interesting and sometimes frustrating.

The -s suffix also appears on verbs to show present-tense action by a single person or thing: “She runs fast” or “The bell rings at noon.” Here it works opposite to nouns: one person running gets the s, while multiple people running don't (“They run fast”).