We're talking about one of the most famous, useful and supported software for electronic design automation (EDA).
Other apps or packages are available to do same: Kicad is free (in sense of free software: code is publicly available), and usually at zero-cost, so that you can start with your projects, from simplest to more professional ones, without any other cost.
Kicad lets you design PCBs (Printed Circuit Boards); more correctly you design the layout - or mask - to stamp on copper board to protect zones of interest from copper removal operation, after which you have the desired electrical tracks.
There's a lot of stuff to talk about Kicad or EDA softwares in general: we now concentrate on a simple step-by-step approaching job, divided in two parts:
- Schematic (design of circuital scheme, creation of netlist);
- PCBnew (layout or mask design to cover copper board).
Just an advice: choose a folder which to put your project files into. Create a folder for each of them, helping yourself keeping files ordered.
Kicad version here adopted is 2011-07-08 BZR 3044 Stable.
Let's begin!