You're in luck, actually: it turns out that Windows 7 includes an entire set of small apps that Microsoft calls "Gadgets", one of which is a clock.
Follow Steps Below:
1.First off, it's as easy as possible to get to the Gadgets: Simply right-click on an empty spot on your Windows desktop, and it shows up in the contextual menu.
2.Select on Gadgets.
3.More options are there like Calender,Clock,etc.
4.Double Click on Clock or Drag and Drop the Clock or Right Click on Clock Add will come and you can add it as your wish.