Great pix, Boomer. Shows the progression and result extremely well. However, as Bill says, it depends on what you're inlaying into what. You use "some tool" : Mill, chisels, knives, dremel, router, etc. to cut a hole in the substrate the same shape as the inlay and then you glue the inlay in and sand it all down to shape. Softer materials like wood are easier than harder materials like metals, but it can be done.