A contour drawing is drawing with no shading or surface texture. Lines are used to articulate the outline and edges of the subject.
The following comes from Freehand Sketching: An Introduction by Paul Laseau, pp. 14-15. Draw for 20 minutes changing the position of your hand as you go. It is ok to put more than one sketch on the same sheet.
Repeat the drawing described above, only this time don't look at the paper. To keep from looking twist your body so the hand you are drawing is to the side. Keep your drawing instrument on the paper. Include detail on the inside, not just the profile of your hand.
An object will be provided in class. Make contour drawings of the object that are roughly double the actual size of the object. Draw for 20 minutes. If you finish the drawing before the time is up, begin another.
Find two or more objects that have complex shapes. Good subjects for this are objects like scissors, kitchen utensils, drafting compasses, etc. Arrange the objects on a surface. Draw contour drawings for 20 minutes.
Construct contour drawings of a sculpture, indoors or outdoors. It's not necessary to draw the context beyond or surrounding the sculpture.
Look for an architectural view that reveals a complex set of contours. Construct contour drawings without attention to lesser details like window frames. Just focus on the shapes of the buildings.