The very very expensive graphics tablets such as Wacom Cintiq have a screen built into the tablet. But they cost thousands of dollars, as you're paying for a graphics tablet and display as well.
Most graphics tablets are just a flat surface that capture the position and pressure of the stylus as you move over the surface. Some capture the tilt of the stylus and other information about it.
That information is sent to an application on the computer which translates the movement and pressure into a stroke, which is displayed on your monitor.
In the case of a Cintiq which has the monitor built in, strokes appear beneath your stylus as you're working.
You might initially find it a bit 'disconnected' to draw on the tablet while looking at the screen. But with a bit of practice you soon get used to it.
Note that with most graphics tablets, you can place a sheet of paper on top, to trace with the stylus around an image you've drawn on the paper.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"