Affixes are groups of letters that are added to the beginning or the end of words to make new words. Prefixes go at the beginning of words and often change meaning, whilst suffixes go at the end of words and often change the kind of word (e.g. from verb to noun, or noun to adjective etc.).
'Substandard' and 'pre-cooked' are examples of prefixes, 'hopefully' and 'happiness' are examples of suffixes.
In the classroom
It is very important to teach affixation as it helps learners guess the meaning of new words they find, and construct new forms successfully. Word guessing games can help develop awareness.