Ahoy sailor, and wellcome aboard
Some quick guide:
Ruler: For measuring distances. It has a 50 yards error built in to represent inaccurancies of real life measuring. Click once to set intial point, drag anywhere you want and click twice to finish. Useful for measuring speed and ranges to/from targets.
Compass: To determine a circle by defining its radius. Useful to stick around a patrol zone or away from known enemy air bases. Click once to set the centre of the circle, drag to widen the radius as much as you want.
Protractor: For angles measuring. Click once to start the first corner, click twice to set the angle link and click for a thirdth time to set the other end. In the centre the angle will be displayed in numbers.
Eraser: To erase any previous drawing from you. CTLR+Eraser deletes all you have drawn previously.
Compass: When open, gives you extra tools in all the previous tools. For example, the ruler comes with an inverted compass that allows determining easily the enemy course.
Hope that helps