there are several good tutorials on manual targeting stickied on the forum, for example:
https://www.subsim.com/radioroom/sho...01&postcount=1
https://www.subsim.com/radioroom/sho...d.php?t=111998
as the old saying goes, "garbage in, garbage out", your solution is only as good as the data you use. The basics are the same whether in sh 3-4-5, you need to figure out the Target's range, course and speed. Once that is done, it is just a matter of plugging it in. SH4 greatly simplifies your task since you have the Target Data Computer which works in game pretty much as it did in RL and will compute the firing solution for you.
One advantage with the TDC is that once you input the target's course in the AOB dial, the TDC will compute the correct AOB. When you rotate the AOB dial on the right of the screen, it will rotate the one on the left of the screen for the target.
For example, in the sub school, the Mogami Heavy cruiser is on a 90 east course, at speed of 9 knots. Use map updates on to double check.
This is from SH3, but discusses the basics:
https://www.subsim.com/radioroom/sho...&postcount=461
Once you get use to the TDC, there is really no limit to what you can do with it. For example, radar only night attack:
https://www.subsim.com/radioroom/sho...&postcount=479