To draw constructions you need a pencil, ruler and a pair of compasses. Loci are used to identify areas that satisfy criteria such as a given distance from a point or halfway between two lines.
To construct a circle you will need a compass, a pencil and a ruler. You need to know the radius or diameter of the circle you wish to construct.
Open your compass to a distance equal to the radius of the circle (or half the diameter). Place the point of the compass at the centre of the circle and lightly draw the shape.