You might want to look at my
"High Realism Tutorial" I've had floating around for a while. I explain many of the concepts you'll need to learn like determining AoB; the function/use of the Position Keeper; how to plot a target on the Navigation Map using the realism option of "No map contacts update"; there's a handy "Speed Chart" and "Worksheet" too.
This revised version, released in 2009, can be used with or without my
"AoB Calculator". A hand held device that will aid in determining a target's bearing and course when at the Navigation Map. There have been several editions of the Calculator since I made it in 2007 (I see Gutted is using it in his Solution Solver), the latest was reproduced by Jerm138 in a PDF form found
HERE.
Along with the Tutorial, you may wish to download the
"Practice High Realism Mission" which sets up the same target the Tutorial uses. Being able to follow along using the same target will get you up to speed in figuring out the mechanics of manual targeting, under a controlled environment. It's JSGME compatible, you just add the mission to the game as any other mod.
As always, read the Documentation for all of the above.
Good luck!