Zoom in to where you made the sighting and click on the exact point on the map.The coordinates are inserted into the latitude and longitude fields on the form.
It is important to get the location as accurate as possible - record your confidence in the accuracy of your location marker in the field provided.
You can fine tune the location by zooming in further, clicking on the marker spot on the map, and dragging it to the correct place.
(NB: The co-ordinate projection is in WGS84 decimal lat/long.)