I'd like to know how a drill works. I kow it sounds stupid but let me explain.

I'm a Mechanical Engineering student and my final year design task involves the design of a modular horizontal drilling unit. a mouthful eh? well, i didn'd to go too far in my head before actually knowing how the whole things works, from the power to the drill rotation. Just a simplified explanation would do, you know.. like the components and what drvies what? It would really help if anybody knew.

cheers!