A simple explanation about the Gerber format. What is it? what does it do? What is the standard?
More on Printed Circuit Boards:
This article explains how you can create a cheap PCB for your electronic circuit and lists some PCB manufacturers.
A few simple PCB design guidelines for creating better board layouts
A step-by-step PCB design tutorial on how to design a PCB layout in Eagle
A tutorial for schematic drawing using Cadsoft Eagle
Tips to minimize the chance of errors before PCB manufacturing