Affixes are used in language to:

Affixes play a significant role in the formation of new words in a language by being attached to root words or base forms. When a prefix is added to the beginning of a word, or a suffix to the end, it can result in entirely new meanings or function changes. For example, adding the prefix "un-" to the word "happy" creates the new word "unhappy," shifting its meaning. Similarly, attaching the suffix "-ness" to "happy" results in "happiness," which converts the adjective into a noun. This process expands the vocabulary of a language and enhances its expressiveness, allowing speakers to convey a variety of ideas and concepts efficiently.

In context, the other options do not accurately describe the primary role of affixes. While affixes can sometimes be used in expressions to emphasize or alter grammar in broader contexts, their main function is fundamentally focused on word creation. Additionally, affixes do not directly play a role in translation between languages. Therefore, the choice that correctly identifies the role of affixes is the one that highlights their ability to create new words.