Navigate to a website -- like Google Earth, GPS Visualizer or iTouchMap.com -- that determines the latitudinal and longitudinal coordinates of any physical street addresses. Most websites work with all locations worldwide, while a few are confined to just domestic addresses.
Enter in as much information about the target address as you know, starting with the street, city, state, etc. Many of these services rely on Yahoo! and Google Geocoding APIs to track down those coordinates.
Wait for the results to come up. Generally, they will be expressed in longitude (x) and latitude (y), which can be further broken down into degrees, minutes and seconds. Most sites also display a map of the coordinates.