Homebrew PCBs

A via is a hole in the PCB that lets you connect copper on different 
layers.  While they're physically the same as the holes for component 
leads, PCB keeps them separate so that you can do things like "select 
all vias" or "increase all pin sizes by 5 mil".

Note that PCB automatically adds vias if you're drawing a trace (line 
tool) and select a different layer (number keys).