Some common prefixes include "de-," "mis-," "pre-," "pro-" and "re-," and some common suffixes include "-able," "-ful," "-ing," "-less" and "-ness." A prefix is a group of letters that appears before the root of a word. A suffix is group of letters that appears after the root of a word.
Prefixes and suffixes change or expand the meaning of a root word. This is evident when reviewing some of the examples above. The prefix "de-" is used to connote a relationship to the root word that is from, down, away, reverse or opposite. So the word "decode" means to decipher a code, essentially the opposite of the root word "code," when used as a verb. The prefix "pro-" is used to connote a relationship to the root word that is for, forward or before it. So the word "proactive" means to take preliminary actions before an event or situation, to act in a forward-thinking manner, in other words.
The suffix "-able" expands the meaning of a root word to suggest an ability related to or possessing a quality of it, such as in the words "comfortable" and "portable." The suffix "-less," on the other hand, creates a word that expresses a condition that is without or not affected by the root word, such as in "friendless" and "tireless."