Start here. It's the SHIV guide.
http://forums.ubi.com/eve/forums/a/t...4351073726/p/1
Longitude lines run across the top of the map east and west, latitude runs on the right of your map north and south. If you get a contact ultra telling you of a convoy at 130.12E by 34.12N, you basically use your tools to find where these lines cross. You can use the mouse wheel to zoom to read more accurate. However, most of these you don't won't to chase unless they're close. The contact report will give you speed and heading, so using that info you have to plan ahead where to cut them off. They're other tools that help you do this such as the nonograph, but I defer to let you search those to learn how.
Here's a good link on L&L
http://www.learner.org/jnorth/tm/LongitudeIntro.html