The word's front and back doors
Add 'un-' to the front of 'happy' and you flip it to 'unhappy'; add '-less' to the back of 'fear' and you get 'fearless'. Prefixes and suffixes are little add-ons that reshape a word.
Front and back
A prefix goes in front (re- = again), a suffix at the end (-less = without). They change a word's meaning.