Graphic Tablet can be used to record everything from your signature, to your handwriting,to original drawings directly to your computer. The usable space on each tablet varies from three to five inches up to a standard eight and a half by eleven inches.
The term "usable space" simply refers to the flat area that you can write or draw on where your creation will be picked up by the computer. Basically a board you connect to your computer and draw on.
The tablet pen functions as the cursor and the board as the screen, when you move the pen to the corner of the board, the cursor on your screen moves to the corner of said screen, etc.