Kicad is a program that allows to manage electronic projects, which includes a complete editor of electrical schemes, called Eeschema, in which the circuits are designed from the different components available.
The components can be: connectors, potentiometers, switches, transformers, capacitors, resistors, and so on. There are libraries for each of these components, but you have the possibility to add new libraries or to modify and extend existing libraries. This is done using the tools called LibEdit.
From a circuit diagram which verifies its correct operation is that a printed circuit will be built, in which the electronic components are adjusted by tracks of conductive material. For that, Kicad includes a tool called PcbNew, which allows 3D visualization of the printed circuit board.
A third tool, called Cvpcb, is the one that allows to associate the components of the scheme with the physical modules of the printed circuit.
Kicad has another tool, called Gerbview, which allows you to view Gerber files that were previously created with Pcbnew. The Gerber files contain the necessary information for the manufacture of the previously designed plate.
There is a video tutorial in Spanish that explains the steps to follow to create a Kicad project; And also a manual in Spanish that teaches in more detail its operation.
There is a forum in Spanish where you can consult doubts and you can access a thread in which you share a library for Kikad.
Kicad is a free program, available for Windows and for Linux. Its last update, 4.0.4, was published in August of 2016.
Download program (Windows 32-bit)
Download program (Windows 64-bit)