As a hobbyist, we often want to extend the functionality of our arduino board. In order to minimize wires and maximize functionality, we design special need-based ‘shields‘. A useful step by step tutorial that I found here , breaks down the process into the following stages:

1) Part selection

2) Prototyping the board

3) Schematic design

4) PCB Layout

5) PCB Fabrication

[Via: krisbarrett]