The easiest way to move your 3D Cursor to that location is by using the

Snap tool (SHIFT+S). Before you trigger the Spin from the Toolbar of

your 3D Viewport, you must set your view from the object to the top.

Press the seven key on your Numpad.

Always consider the plane where your Spin will occur. The view you

have must be perpendicular to that plane. In our case, the Spin happens

in the X and Y-axis plane. For that reason, using the Top view is the best

option.

What happens if you don't change the view? The Spin will use any

perpendicular projected plane, based on your current viewing angle.

When in the top view, press the Spin button. A blue arc appears close to

the selected elements. Click and drag your mouse above the arch, and

you start to see your round shape appearing. At the Spin options on the

lower-left corner, you can control the rounded shape's rotation and steps

(Figure 4.31).

Figure 4.31 - Spin shape