[magic452]

To expand on what Loudspeaker said.
When you get a contact on the map just mark that spot with an X and start the stopwatch. Wait 3 minutes (or 3 minutes and 15 seconds for metric) and mark an X on the new position, wait 3 more minutes and mark another X.
Draw a line through the Xs and extend the line to show the targets course.
Measure the distance between the first two Xs and that distance will give you the target's speed. 1,000 yards or meters equals 10 knots. 500 yards = 5 knots, etc. Check the speed with the second and third Xs, should be the same. If a little different measure the distance between the first X and the last and divide the distance by two to get speed.

If the target is a sonar contact you will see a line from your boat, mark the X at the end of the line.

If the target is a visual or radar contact than mark your X at the target icon.

If the contact is more than 20 nm away and does not move, that is a radio report and for someone just starting out I would suggest that you just don't pay any attention to them, you will drive yourself crazy trying to find them as they won't be there when you get there. If you run the mouse over the contact it will give you the direction of travel (heading) and speed,You'll learn how to do this when you get more experience.

I'm goin' Down gave you some good advice, the Bag of Tricks has a lot of good information in it.

Magic