Welcome aboard kaleun
-Targeting
You can specify manuar or auto targeting in the realism options screen. Before starting a mission click "realism settings" (or something like that).
With manual targeting you'l have to: identify the target, estimate speed, range and AOB by yourself. It's a bit tricky, but practise makes perfect.
A great AOB won't give you a good shot by itself. You have to be aware of other things to, like the distance (in my opinion best distance to fire is between 1000 and 300m) and what torpedo you're using and whether you are using magnetic ir impact trigger.
Before a mission in campaign check the availlable torps and their specs to deside wich ones to use. you can check this forum about threads for "newbies"
and remember. PRACTISE PRACTISE PRACTISE
-single mission 2
Bad weather is a challenge.
You can use the periscope but it's a bit harder
In high weaves you can't use the deck gun and flaks.
-night missions or ports?
what cool things do you mean?
-ramming
about that you simply have to be more carefull
more missions for SH3
you can find missions and some cool mods here:
http://www.subsim.com/subsim_files/patches2005_sh3.html
Good luck and good hunting kaleun