to inscribe a square inside a circle first you must draw a diameter anywhere across the circle. what should your next step be?
a. construct a perpendicular bisector.
b. draw a second diameter to the circle.
c. construct a line tangent to the circle.
d. set your compass the length of the radius.

1. Find the center of the circle. (See source for a method how...this method for finding the center of a circle will actually get you through steps 1-3.) 

2. Draw a diameter of the circle. 

3. Draw a perpendicular bisector to the diameter (this will be extended to form a second diameter). 

4. If a diamond tilted square is okay, just connect the four points of intersection with your circle...otherwise: 

4. You should have 4 right angles in your circle. Draw angle bisectors to two of the adjacent angles, and extend them through the circle (Link for this also given below). They should each intersect twice, giving you the four vertices of your square. 

5. Connect the vertices, making your square.