“pcb” is software to help you draw (“lay out”) the wires for a custom “printed wire board” (“PCB”).
“Out-of-the-box”, pcb supports 16 copper layers. It has been patched by some users to support more, however.
This is well beyond the scope of this FAQ. There are a few tips at
See PCB footprints.
There are also some unofficial gEDA footprints at Open Circuits http://opencircuits.com/PCB_Footprints.
The application is a fairly old project, with roots way back in the era of Atari home computers. Its name has always been “pcb”. The current developers have no intention to break that tradition.