AA guns are automatic (unless you press P to toggle them - good idea if you are trying to stay stealthed in a destroyer).
Torps get fired in the same way as the main guns but you have to select them (by pressing 3 on ships equipped with them). Make sure you select your target by 'looking at it' and pressing x. That way you get the grey targetting aid.
Key thing is don't get spotted first, be in a position to support and generally stay together ! Plus DON'T forget the map objectives, I see so many games lost as people chase down the aircraft carrier and ignore the capping.
Lastly you'll see people refer to ships by the following:
DD - destroyer
CA - Cruiser
BB - Battle ship
CV - aircraft carrier
Have fun