* Contractions combine two words into one by replacing some letters with an apostrophe. For example, "do not" becomes "don't", "I will" becomes "I'll", and "they are" becomes "they're".
* Possessive nouns show ownership by adding an apostrophe and an "s" (or just an apostrophe if the noun is plural) to the end of the word. For example, "the dog's bone" or "the girls' toys".
Both contractions and possessive nouns use the apostrophe as a signal that something is being combined or altered, which makes them similar in their function even though they are used for different purposes.