A compass is the traditional hand-tool for sketching circles and arcs. Its scissor-like configuration consists of two points: one sharp needlepoint and one pencil point. Natural tension or a tightening-screw in the hinge maintains a fixed angle between the two legs. A clamp usually holds the pencil point firmly on its leg. With the needle acting as a pivot, the pencil point spins evenly around it to create a perfectly smooth circle.
Close the compass legs, one against the other, and align the tip of the pencil with the needle tip. Tighten the pencil's clamp to hold it firmly in place.
Set the radius of the circle by opening the compass along a ruler. The distance between the two tips will be the radius of the circle. Some compasses have angled markings on the hinge itself for setting the radius. Tighten the tension in the hinge to keep it firmly in place.
Place the needle tip where you want the centre of the circle to be. Press down on that leg while spinning the knob on top of the hinge in order to spin the pencil around the needle and make a perfect circle.