What does an apostrophe ' mean and when is it used?

An apostrophe is used when one or more letters has been removed from a Word, or when two Words have been combined; except for the possessive adjective "its." Horse Isle :) JumperGal riding Sonic :) Dude/Dudet thx this rlly helped me cuz i have a quiz on Apostrophes so just th CTG (>.>) <(0.0)> (<.<)