This construction assumes you are already familiar with Constructing the Perpendicular Bisector of a Line Segment.

After doing this	Your work should look like this
We start with a given circle.
1.  Using a straightedge, draw any two chords of the circle. For greatest accuracy, avoid chords that are nearly parallel.
2.  Construct the perpendicular bisector of one of the chords using the method described in Constructing a perpendicular bisector of a line segment
3.  Repeat for the other chord
4.  The point where the two lines intersect is the center C of the circle.