Apostrophe

After so many years of not caring I realised today that I have no idea how to use an apostrophe outside of shortening "it is" or "is has" to "it's" type of thing.

So good old wikipedia to the rescue :-) I just spent the past 10 mins reading up on it and have found out that it's all about possession and plurals.
's indicates possession
s' indicates plural

So for those of you who have also gotten rusty on your primary school english lessons are some examples from wikipedia (http://en.wikipedia.org/wiki/Apostrophe)

To illustrate that possessive apostrophes matter, and that their usage affects the meaning of written English, consider these four phrases (listed in Steven Pinker's The Language Instinct), each of which has a meaning distinct from the others:

• my sister's friend's investments
  (the investments belonging to a friend of my sister)
• my sister's friends' investments
  (the investments belonging to several friends of my sister)
• my sisters' friend's investments
  (the investments belonging to a friend of several of my sisters)
• my sisters' friends' investments
  (the investments belonging to several friends of several of my sisters)

Kingsley Amis, on being challenged to produce a sentence whose meaning depended on a possessive apostrophe, came up with:

• "Those things over there are my husbands."
  (I'm married to those men over there.)
• "Those things over there are my husband's."
  (Those things over there belong to my husband.)

So I can assure you that I will still much it up sometimes. But at least now I have a way of working out what should be the correct use of the '

Right Paul - no testing on this one at home ok ;-)