This rant will almost certainly be expanded at some point, but for now, one of my pet hates....
OK; this punctuation mark is one of the most misused in the language, which is *so* frustrating for those that care, because they're actually
very easy to use correctly - look at this:
1, Apostrophes indicate *possession* or missing letters; they *never*, *ever* indicate a plural, even where the item is an abbreviation, thus the
correct plural of 'photo' is 'photos' and the correct plural of 'CD' is 'CDs'.
2, It is correct to say 'John's dinner' because the dinner belongs (in a grammatical sense) to John. Where the word ends in 's' eg. James, then there's a choice
one can either add an apostrophe after the 's', or one can add both an apostrophe and an additional 's'. It doesn't really matter which you do - go
for the one that looks and sounds best in the circumstances.
3, Where the possessor is plural eg, elephants, children, then the apostrophe goes after the final 's' eg. 'the elephants' tails' (when referring to
the tails of more than one elephant. Where the plural doesn't end in an 's' eg. children you add both an apostrophe and
an 's' to the word, so it's 'the children's game'.
4, You just have to learn this bit; like most bits of English grammar, there are exceptions to every rule, and one of the confusing ones in this area is 'its' and 'it's'.
Its means 'belonging to it' - so 'the field was cold and damp; its trees dripped.' 'It's' is the contraction of 'it is' - so 'It's a sunny day' is correct.