The Oval tool will draw an oval or a circle.

Click the Oval button

Click to set the first point.

Hold the mouse and draw down and to the right.

Click to set the end point. 

• Left-click sets the point under the cursor.

• Hold down the CTRL key while dragging the mouse to draw a circle.

• Ovals have four control points.

If Auto Align Circuits has been selected under Options, you will see blue highlights in the form of lines and circles when the cursor is aligned with another control point, end point or center point of another object on the design as you are editing. 

If is too distracting while working on the current design, this can toggled off under Options.