Wow, thanks guys, I'm amazed at what a helpful community this is, never seen anything like it. I really appreciate it.
I've managed to get through the first 2 tutorials now, I was going to try the next ones but my butt was getting sore.
Edit: Argh! I just tried the torpedoes tutorial and it's impossible. There's just too many things happening at one time for me. Correct me if I'm wrong, but my torpedoes will go where my periscope is pointing at 0 degrees? So the other ship is moving, I'm moving, I have to be pointing straight at it, all in a short space of time to press 'fire'.
So eventually I managed to get all this figured out and got lined up with the ship I was hunting. The targeting arrow over it turned green, so I assumed that meant if I fired it would hit it. So I fired two torpedoes...but nothing happened. I looked in free view and one of them was pointing down, below the ship, not moving, and the other seemed to have gone under the ship and was speeding on past it.