To use the widget on Android 4.0+:
- open the app drawer
- tap the "Widgets" tab
- find Xperia Clock Widget and drag it to the home screen

To use the widget on older versions of android:
- long press an empty spot on the home screen
- select "Widgets"
- tap on Xperia Clock Widget to add it to the home screen

NOTE: If you are using a Task Manager make sure to add Xperia Clock Widget to the ignore list. When the app is killed the time will stop updating.

Sony Xperia Clock Widget
Xperia One Clock Widget
Xperia 10 Clock Widget
Xperia 1 Clock Widget