Why does a pen have ink in it?

Pens do not contain ink, they contain paste. In a ballpoint pen, the paste is made up of a mixture of oil and pigments, which is held in a reservoir and released through a ballpoint at the tip of the pen. The ballpoint regulates the flow of paste and transfers it to the writing surface when pressure is applied. Fountain pens, on the other hand, use a reservoir of liquid ink that flows from the nib onto the paper.