We can use Inkscape to create an icon by following this steps...
- Download, install and open Inkscape
- Open document properties and set width and height to your desired size
- Outline your icon by using the "Draw Bezier curves and straight lines" tool, "Edit paths by nodes" tool, and "Select and transform objects" tool
- Set fill and stroke colors of your icon by using swatches (I usually use the Tango Icons palette)
- Shade your icon by using linear or circular gradiant fill
- Finally export your icon to a PNG file by using File->Export Bitmap... then select Page, enter width and height, click Export
http://inkscape.org/