To use Chronus all you have to do is pick a widget. Usually this just involves holding down on your home screen for more than one second and picking which widget you want to use. You can then access the customization options for the tool you've selected.
The weather widgets, perhaps the most popular alongside the clock ones, use info from Yahoo!, OpenWeatherMap, Weather Underground or Forecast.io. In the setup options you can set which source you want, as well as the update interval.
Chronus is a great set of widgets for Android, thanks to which you can customize your device to quite a remarkable extent. A super interesting option whether what you need is a simple clock on your homescreen or management of your email and notes with just a glance at the screen of your device.
Requires Android 4.2 or higher.