To construct a circle, draw a line that represents the diameter of the circle. Bisect the line so that it is a perpendicular bisector of the diameter of the circle. Place your compass at the bisection point/midpoint and draw an arc or better still the whole circle.
Theorem: the perpendicular bisector of a chord passes through the center of a circle.
Note: a diameter of a circle is a chord that passes through the center of a circle.
