If you want to draw the circle using snaps, make sure that the End Point Snap and/or Between Ends Snap are turned on.
Position the cursor at a point on the circle’s circumference. Press down your left mouse button. Holding down your left mouse button, move your mouse. As you move your mouse you will see the circle being drawn. When you are satisfied with the circle, raise your left mouse button.
Click to undo.
If the circle is displayed as a dark blue outline or as a green filled shape, vectors are set to display by type. Press C to toggle between displaying vectors by color or by type.