Enter an address (or just a zip code) into the "address" box above, along with a radius for the circle in miles and press the "process" button.
The resulting polygon represents a circle with the radius specified at the coordinates of the address. You can drag the circle anywhere by moving the center marker, enlarge or shrink the circle by dragging the radius marker (green) or change the circle into an irregular polygon by dragging any of the other markers (nunbers 1-12).
You may remove the polygon at any time by clicking on the "Clear Radius" button, this will leave any zip codes that have been selected to show a "clean" map of just the zip code areas.
Next, click on the "Get Zip Codes" button to retrieve the zip codes for the that area. Hovering over the link will cause the opacity of the image to change, clicking on it will toggle the color. Click on the small yellow square in the image will bring up a change window.
Some zip codes may display only in the sidebar, without a link and be marked with '(point)'. These are 'Point Zip Codes' or zip codes that can only be indicated as a single point, such as P.O. boxes, APO's or single building (or corporate) zip codes.
There is a limit of 100 zip codes pulled per search, so keep that in mind when setting your radius.