When drawing contour lines on the map, you are drawing a special class of freehand object. Drawing it is the same as for a freehand outline (see 'adding other types of object') but the 'settings' window is a bit different:

The colour, style and width are as for the 'object outline' colour, style and width on other types of object (see 'Changing other types of object').
Additionally, for contour lines, you can specify that you want to show height figures on the contours. These will appear around the middle of the contour line or if it snakes around, every time it crosses the centre point of the added line (see below). The height shown is that entered on this screen.

Clicking 'OK' will save these details, clicking 'cancel' returns the details to the state they were in before opening this window.