This window lets you select coordinates (latitude and longitude) for sunrise and sunset estimates by clicking on a world map, or on enlarged regional maps as selected from the popup menu at upper right. Location data are accurate only to 0.33 degree of longitude and 0.25 degree of latitude on the world map and 0.11 degrees of longitude and latitude on the regional maps, but that should be accurate enough for most sunrise-sunset calculations.
As geographic references, the maps show the equator (yellow), the Prime or Greenwich Meridian (zero degrees of longitude), the Arctic and Antarctic Circles (~ 66.5 degrees N and S), and the Tropics of Cancer and Capricorn (~ 23.3 degrees N and S). Only a few of these will be visible on the enlarged regional maps.
To select coordinates, move the cursor to the desired location and hit either the spacebar or the return key. The 'Longitude' and 'Latitude' boxes will update continuously as the cursor moves within the map area. When you hit the spacebar or return key, the selected coordinates are shown in the 'Selected position' box; to change these, move the cursor to another point and select again.
Of course, if you want higher precision coordinates, use Google Earth.