1. Suffixes: These are letters or groups of letters that are added to the end of a word to change its meaning or grammatical function. Some examples:
* -ing (present participle): walk -> walking
* -ed (past tense): walk -> walked
* -ly (adverb): slow -> slowly
* -ness (noun): happy -> happiness
2. Prefixes: These are letters or groups of letters that are added to the beginning of a word to change its meaning. Some examples:
* un- (opposite): happy -> unhappy
* re- (again): read -> reread
* pre- (before): game -> pregame
* mis- (wrongly): understand -> misunderstand
3. Inflections: These are changes to a word's spelling to show grammatical function. Some examples:
* -s (plural): cat -> cats
* -'s (possessive): cat -> cat's
* -er (comparative): big -> bigger
* -est (superlative): big -> biggest
4. Compounding: This is when two or more words are joined together to create a new word. Some examples:
* blackboard
* smartphone
* raincoat
* heartbeat
It's important to note that adding to words is a complex process that involves understanding the word's meaning, its part of speech, and the rules of English grammar.
Do you have any specific examples in mind where you are unsure when to add to words? I'd be happy to explain!