I have Dell Inspiron laptop and I have just started using Photoshop. It is quite hard to draw using mouse so I was thinking of buying a digital pen. Do I need a special laptop with touch screen to draw or how can I make it work?
You cannot draw on the screen itself if it didn't come as a touchscreen. The only dell models which are touchscreens are a few of the Studio laptops (not most of them) and the Latitude XT.
One alternate option is to get a digitizer tablet, which is an external tablet without a display that you can write on. It's less intuitive than drawing straight on the screen, but gives you much more precision than a mouse or touchpad.
Wacom is one of the main manufacturers for them, though there are others as well. Do some looking around to find what might work for you, and if you can, try one out in person before buying. A quick google product search might get you looking in the right direction.