Posessive aspostrophes

Right you are. You just add an apostrophe to the end of the word when it ends with S, I do believe.
I'm learning Danish now and there is a bigger problem there, that is in Danish possessive form of name is i.e. Robert + s; without apostrophe. So Danes have problem writing the possessive form of Rasmus which is the name of many of the Danes.

When saying one of the s' words, you still pronounce the second "s", even if it isn't actually there. For example, "Socks' toy" would be pronounced "sock-siz" (which is basically your first example).

I was always taught that one should use 's whenever the owner of the possession is singular. So "Socks" the cat would be the owner of Socks's toy.

In "modern usage" I've read that it's acceptable to omit the final s, although that still doesn't sit right with me!

I was always taught to write just the apostrophe after the S even if it is a singular word (e.g. James). So instead of James's radio, we have James' radio and as there is no S after the apostrophe, we don't pronounce this phantom S.

Though it is considered ok to omit the final s, it is still not correct grammar to do so. Many college professors will reduce your grade for it.

I was taught that one shouldn't try to teach others if one doesn't know what one is talking about. Something that, I seem to remember, I actually taught myself so I s'pose I could be wrong.