I don't know what its called, I am an artist & i need a tool to make sketches on my computer screen & then maybe edit them on photoshop. Someone told me its called a smartpen or a tablet pen or a styler. How many types of such pens are there & what are they called?

What you want is called a tablet. It plugs into your computer, probably via USB, and you write on it with a thing called a stylus, which is basically just a piece of plastic. What you write on the tablet appears on the computer screen. There are other types where the pen is the active componant and you just need a hard surface to write on. A bit like a mouse only you can draw pictures. A search of google will get you many options. Stuart

Check Wacom at: http://wacom.com/index2.cfm

In addition to the tablet there are also touch screens, and also real light pens that read the light off the screen. They vary in sensitivity and resolution. The last light pen I had was run off a CGA card that had a built in interface. It could resolve to the nearest pixel. Touch screens are usually set up for coarser resolution as a finger is usually used.