the apostroph is placed if it describes the belonging of somebody. steve's car. but if you do it in plural, you do it without apostrophe: alot of steves.
Regarding the correct use of apostrophes, I always refer to
this. (Not directly related to this topic, but still a nice link to post).
There's also one on the correct usage of "their" vs. "they're", but the one thing that really bugs me is the phrase "I could care less". I
know it should be "I couldn't care less", but people say "I could care less" instead all the time. But that is wrong! It implies that it is possible for you to care less, thus you must care at least to some degree!
WHAT TO BELIEVE ANYMORE IN A WORLD LIKE THIS