The apostrophe of possession shows belonging, e.g. the house belonging to Ryan is Ryan's house. Making a singular noun possessive is very straightforward, but you would be surprised how many people make mistakes with this punctuation mark! With singular nouns, take the word and add an apostrophe plus an -s. So you can make such possessives as these: crocodile's teeth, baby's blanket, light's brightness; dentist's office; Lucinda's bike; book's pages, etc.
What do you do if the word ends in an -s already? For example, how would you write about the shortage of storage space on the bus? Ready? You could write this: the bus's shortage of storage space was always a terrible inconvenience for anyone arriving home from the airport. Notice that even though "bus" already ends in an -s, you would still add an apostrophe plus an -s. People's names ending with an -s can be a little trickier. It is considered correct to write "James' pen" or "James's pen" (and if you think about it, this would be pronounced with two s sounds: James-s pen...). So when it is a name ending in an -s, it's your choice!
Try our English quiz on apostrophes of possession to sharpen your mind.