Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), used to be reserved for a layouter in the company sitting on a pedestal in front of a workstation running thousand dollar software. Anyone wanting to make a printed circuit board (PCB) were reduced to using overhead projector slides and kitchen skink photolithography and etching. Not anymore. Open source projects have produced software which is free, not just in the sense that it does not cost anything but the files are in readable text format, not some proprietary hex code.
There are several projects, but I will mention gEDA and KiCad.
gEDA started out as a shortcut to getting a PCB fabricated from standard GERBER file outputs. It still is that shortcut, but the project is not well-supported at present. You can still install and use it, if you have some persistence. KiCad is kind of an OrCAD clone. It is a more active project and can be installed on most operating systems with a few clicks.
I did not work with PCB design originally, I came from the optics side of things. There comes a point when you try to solder a photodiode at the end of a coax cable, and you think, there must be a better way. I have had the privilege to work with electronics engineers who were responsible for the PCB design. It turned out that the easiest way of specifying what you need is by drawing the schematic. Paper and pencil works, but if you have to look up how an nMOSFET is drawn it is so much easier to use the EDA where the symbols are ready to drop in.
Electronics design was a well-thought-out process even before EDA. Picture the function in an abstraction, the schematic, use that to analyze and optimize, then add concrete values and IC models. Each discreet component has a reference designator (refdes), bundle the value and model to the refdes as an attribute, last specify how the component is going to look on the PCB, its footprint.
With the schematic and component attribute, footprint and their connections, the netlist the design can be brought to the PCB. In the PCB design we have a physical 2D representation. Here in the PCB editing we do the layout, which can be broken down in placing the components and routing the design, which is drawing copper tracks ensuring the connections in the netlist (ratnets).
Links
Kicad project page https://www.kicad.org/
Kicad download https://www.kicad.org/download/
gEDA project page https://geda.sourceforge.net/ https://en.wikipedia.org/wiki/GEDA
new gEDA forks lepton-eda https://github.com/lepton-eda Schematic editor, pcb-rnd PCB layout http://www.repo.hu/projects/ringdove/download.html