A prefix is a word part added to the beginning of a word that changes the word's meaning (ex: preheat = heat before). A suffix is a word part added to the end of a word that changes the word's meaning (ex: hopeful = full of hope).
Root Words, Prefixes And Suffixes Explained for Parents
Blog post about prefixes & suffixes as well as several printable activities
Another blog post about prefixes & suffixes with lots of suggested activities and free download
Variety of online games to practice prefixes & suffixes
More advanced online games to practice suffixes