Set location by lat/lon, or by map
The next time you add / edit a place or an image, you'll see latitude and longitude fields where you can type in their values directly. This will be most useful for readers like T who are using GPS devices to record their position.
You can still set the location by clicking on the map: the latitude & longitude fields will automatically update to display the correct values for your marker's position.
Alternatively, type values in to the latitude & longitude fields, and a marker will be automatically displayed on the map at that position. (The marker is only displayed / updated when you leave the Latitude / Longitude fields, eg by pressing the Tab key to move to the next field).