A compass is a drawing instrument used for drawing circles and arcs. It has two legs, one with a point and the other with a pencil or lead. You can adjust the distance between the point and the pencil and that setting will remain until you change it.

Along with a straightedge, the compass is used extensively in constructions, where geometric operations are carried out by drawing only, with no calculations involved.
See Constructions using a straightedge and compass

This kind of compass has nothing to do with the magnetic compass used find the north direction when you are lost.