It’s sometimes difficult to know with an apostrophe where its proper place is. The answer is that you put an apostrophe in a word to show that letters have been left out. We call these words “contractions” and we use them a lot in daily speech. If you have trouble with apostrophes, it is possible to go your entire academic career without using them. In fact, contractions aren’t generally considered appropriate most of the time in formal, academic writing. (We try to keep it somewhat casual ‘round here.)
“But,” you might be thinking, “what about using apostrophes to show possession?” Well, the truth is that possessive forms that use apostrophes are contractions as well.
Example: That one is Jayne’s hat.
The expanded version would read, “That one is Jayne, his hat.” There is no feminine possessive form in English. So if you aren’t sure whether or not to use an apostrophe for possessive, ask yourself if it would still make sense if you put the word “his” in place of the noun. If you can, it’s possessive.
The only real tricky word is “its.” The problem is that “it’s” is already a contraction of “it is” and it would be confusing if “it’s” also meant that something belonged to “it.”