For instance, I just used "it's" as a contraction for "it is." That's simple and follows the rules for contractions: if you leave out some letters, replace them with an apostrophe.
Then there's the word "its" without the apostrophe. "Its" is a word that is used as the possessive form of "it." Usually when indicating possession, the normal rule is to write the noun and make it possessive by adding an apostrophe and an "s." The word "its," which shows something that belongs to "it," is an exception. To show that "it" possesses something, you leave out the apostrophe. This confuses a lot of people, and I used to be one of them. Then I got tired of being confused about using or not using an apostrophe with "its" and "it's" and looked up its proper use.
People get confused about the apostrophe and "s" when indicating possession, especially when the noun is plural, like "men." You'll see signs in some establishments indicating the "Men's Room." Some establishments with that sign have a corresponding sign for the "Ladie's Room." "Men's Room" is right; "Ladie's Room" is wrong. Many places have signs that just say "Men" for one and "Women" for the other, avoiding confusion, but a few places still like calling women "ladies" so they have one sign that says "Men" and another that says "Ladie's." Nice try.
Then there's our way of writing about decades using numbers. Possible choices are "the 60s," "the '60s," "the 60's," or "the '60's." The second one is correct. The apostrophe takes the place of "19" and the "s" indicates the plural nature. Of course, you could avoid the whole thing and write "the Sixties."
Recently, while using StumbleUpon, I saw a page that lays out the proper use of the apostrophe. It's a handy page if you find apostrophes confusing. It was long after high school before I felt confident about using