The suffix "er" is commonly added to verbs to form nouns that indicate a person or thing that performs the action of the verb. For example, in the word teacher, "teach" is the verb, and adding "er" designates someone who teaches. Similarly, in runner, the suffix indicates a person who runs. In addition to people, "er" can also describe objects associated with an action. For instance, a blender is a device that blends. This suffix helps create a clear connection between the action and the subject, making it easier to understand roles and functions in language.