v1.3 of SH4 will do for you for now, though the Uboat Missions "Add-on" is better. SH3 is also good. I played both "stock" for the longest time, back when... If you do go to mod either of them later, you will run into the Windows versus Steam "security" issue, and you will have to move your installs from the C:\ Program Files folder to a different Steam "Library" folder that Windows won't interfere with. For now, at stock, you're good for either game. While SH4 is US subs, and SH3 is German subs, there is nothing in either that would impede your understanding of what is going on. In the "Support" folder in the game's root ("C:\Program Files (x86) \Steam \Steam Apps \common \Silent Hunter 3\Support") is the "Silent Hunter 4 Manual.pdf". In SH3, it's the "Documentation" folder instead of Support, and it's "SH3 Manual EN.pdf" (if you're English speaking, "_DE" if German). In SH4, there's a front and back Quick reference jpeg files for keyboard shortcuts, and in SH3 that would be a "QRC.pdf" file in the Documentation folder. Those can all help you come to grips with the games.
At the top of page for this section of SubSim is THEBERBSTER's
SH4 <> TUTORIALS <> HOW TO DO IT <... thread, and Rockin Robbins
Sub Skipper's Bag of Tricks, both of which have info for from beginner to expert.
The main things for you, the observation periscope is larger in diameter, so as to pull in more light, especially for night use. It is seen much easier by the enemy. That is why when you press the periscope "hot key" (F4 in stock SH4), you default to using the attack periscope, which is much smaller in diameter. Even with that though, at a 2/3 speed, you attack periscope would be throwing up a pretty good rooster tail in the water, so you need to slow down to at most Ahead One Third. Pressing the "P" key will put you at periscope depth, which allows for the smallest profile of your periscope, except in rougher seas, when you might have to come up a few more feet. Even with all of that, unless you're shooting, you want your periscope up as little as possible. Quick, short peeks, make your map marks, then bring it down asap. If you click and slide-out the left-hand tab of the PK portion of the torpedo targeting system, you'll see a couple of boxes towards the top that will hold the ship identification and the range when you are on auto-targeting. You want to be as close as you dare when you shoot, generally 900-1500 yards, to minimize the possibility of the target seeing the torpedo tracks, and avoiding them with a speed change and / or course change. Sometimes though, shots from further out are necessary due to the escorts.
Use the <Q> key to open the torpedo tubes before you try to shoot, and use the <W> key to cycle from tube to tube in sequence. Oh! the blue lines means a warship has been detected on your sonar, the line indicating the direction of detection. The black ones are either unidentified, or merchant vessels. The red lines are the direction that a sonar ping is coming from - if my memory of stock isn't failing me...