Welcome aboard Bugsy
http://www.subsim.com/radioroom/showthread.php?t=229368 will help you to learn how to manually target ships and fellow Subsim member Aktung also had originally posted this targeting geometry illustration from wilkepedia,
https://en.wikipedia.org/wiki/Torpedo_Data_Computer
TheBerbster is also a font of knowledge in this area as well. The Silent Hunter series has the benefit of scaling how realistic and challenging it is to play, thus, you can have fun playing the simulation whille still learning it's intricacies. Once again, welcome aboard and enjoy your sims. Welcome aboard as well fld.