To set your location, select the icon at the bottom left of the main screen, and from there search for a specific place or postcode. If you agree to the disclaimer in the settings (see below), you can also use the device to locate itself, using GPS or WiFi. While locating, the current accuracy is shown, and when it is good enough, select Save.
Selecting the location itself will switch between OS or Irish grid reference, and latitude and longitude.
You can also set your location to a place or UK postcode. Simply enter these into the search box and select Search. If a match is found, choose it and select Save.