Use the Ellipse tool
Use the Ellipse tool to draw circles or ovals.
To draw a circle or oval
In the Toolbox, select the Ellipse tool.
Using the Ellipse tool, drag in your document. To constrain the shape to a circle, hold down the SHIFT key.
If you hold the ALT key when dragging, the ellipse will be centered on the point where you originally clicked. Holding down both SHIFT+ALT will center a circle on that point.
The resulting path consists of Bezier curves and anchor points that you can edit to create nonelliptical shapes.