The site should automatically calculate your home Lat and Long once you have entered your home address details and clicked register. You can however override these calculated values by entering your own using a decimal degrees format in the Lat/Long fields (e.g. 51.341551 -1.936684).
It's easy to get from Google Maps by right clicking on your home location and then clicking on What's here?. The Lat/Long will appear in the search line above the map in the correct format so just cut and paste these into the Lat/Long fields.
If you already have an account, you can log in here.