Can anybody help me figur out how to operate the bloody sonar? The tutorial was pretty much useless. My main problem is stimating how many times the contacts propellor spins or some stuff like that. Any other info on the sonar would be helpful.

If you mean how to get Turns Per Knot value in DEMON sonar then check it in USNI Reference (key shortcut F11) by choosing supposed or known from narrowband sonar signature ship class you detected, TPK value should be in the top of class description. Then you can read speed of contact (leftmost line in demon), useful for TMA and nuber of blades in the propeller (number of lines), useful for contact further identification (check number of blades for supposed contact class).