You add widgets to the home screen by pressing on an empty area on the home screen till a widget menu appears. Scroll down in the widget till you find the Snowstorm entries. Select the size that you want to install.
A newly installed widget isn't configured, so you need to tap on it, and then configure it. The default settings are normally ok, so just press save.
The widget will then try to download a forecast for the current location. Downloading can take about a minute, or longer if the Yr servers are heavily loaded.
The widget will keep trying to download a forecast periodically if the Yr servers are down, or if there are any problems in getting your current location.
You can see a detailed forecast if you tap on an installed widget.
You can see a log of what the widget is doing by tapping on the widget, pressing menu in the forecast view, and then selecting log.
You can always change the widget settings by tapping on a widget, pressing menu, and then select settings.
Start Snowstorm, and select the search or recent tab. The search tab will let you search for a location, and you can then view a forecast for the selected location (if Yr has one). The recent tab will display a list of locations that you have retreived forecasts for, and you can also see when you last downloaded a forecast.