A Prefix is a word that is added at the beginning of the root word to form a new word. A prefix word does not have any meaning of its own but when added to a root word it modifies the meaning of the word. Prefix makes a word negative, indicate opinion or show repetition.
Dis (Prefix) + Agree (Root Word) = Disagree (new word)
Like Prefixes, Suffixes are also words that are added to the root word to form a new word but suffixes are added at the end of the root word. Suffix does change the meaning of the word it is added to but not make the word opposite or negative as prefix do, it simply changes the class of the root word like a verb is changed into an adjective by adding a suffix.
Agree (root word) + Ment (Suffix) = Agreement (New word)