A pen is a common writing tool, usually composed of a pen stem and a nib. The stem can be made of wood, metal, or plastic, while the nib is usually made of metal. There is usually a small hole at one end of the nib for storing and releasing ink. When used, the ink flows out of the small holes, allowing the nib to leave ink marks on the paper. There are many kinds of pens, common pens, ballpoint pens, pencils and so on. A pen is a pen that uses ink to write, its tip is usually sharp, and a certain amount of pressure needs to be applied when writing. Ballpoint pens use a special kind of ink with a small ball built into the tip that rolls and releases the ink as you write. The pencil is a pen that uses a lead lead to write, and its tip is usually smooth, and only needs to be lightly smudged when writing.