Prefixes are special groups of letters added to the beginning of a word to change its meaning. For example, the prefix un- means "not," so when added to the word happy, it creates the word unhappy, which means "not happy." Other common prefixes include re-, which means "again," as in redo, and pre-, which means "before," as in preview. Using prefixes can help us understand and create new words easily. They allow us to modify existing words to express different ideas. For instance, adding the prefix dis- to agree forms disagree, meaning to have a different opinion. By learning prefixes, we can expand our vocabulary and improve our communication skills.