Since you are actually teaching your Dad how to play and he is too embarrassed to ask these questions, we will gladly help
just kidding!
Welcome aboard Herr Kaleun!
In regards to manual targeting: reading the book by Dick O'Kane about his service on the Wahoo, he actually explains how he learned to judge angle on the bow which is the hardest to explain via words.
Before I get spanked for mentioning a fleet boat commander's strategy within the context of U-boots, you can achieve this by doing it in game as practice.
He actually took model ships and fastened them to a board in such a way that they could be angled slightly with your hand. He set up a pair of binoculars some ways away from it and started to judge AOB be sight alone, which was the case in real life.
The way you do this in sh3 is set for auto targeting. Once you hit 'lock' button in the torpedo station, the target ships heading, speed, aob and its bearing relative to your boat is calculated. If you use OLC's GUI, it has a nice feature in that the dials are hidden until you hit the button to bring them up. Before you bring them up make your own observations and on a piece of paper draw an exaggerated long triangle representing the ship and using the top as the bow of the ship draw it in relation to what you observed. When you get good at being able to pick that out then you take the next step and start calling out the numbers. When that happens hit us up again for step two