Welcome Friz to Shmups.org site,
I'll gladly answer your first question:
A PCB is a shorten term for Printed Circuit Board, hence the PCB initials.
You would use a PCB just like a normal console game cartridge and just plug it into a 56-pinout standard Jamma harness (that is assuming if said PCB is standard Jamma class anyways -- there are several different classes of Jamma standards these days) and plug the supergun into a analog CRT-based RGB monitor, a regular old school CRT-based NTSC (or PAL-based one if you reside in Europe) TV monitor setup or if you have a CRT-based SVGA PC monitor (in conjunction with an upscan convertor device like the XRGB-2) depending on the various video outputs that are coming out from the supergun.
What is a supergun you might ask?
It's basically the inside guts of an arcade cabinet setup all rolled into a smaller and more compact box with it's own power supply unit (PSU), plug in your favorite D-pad or arcade joystick controller to play your favorite arcade PCB games like it was meant to be. ^_~
Here's an example of a PCB based supergun setup courtesy of fellow shmupper rolins:
http://shmups.system11.org/viewtopic.php?t=22462
If the said supergun has outputs for RGB, Component Video, S-Video and/or Composite Video, then it will be easier to choose whichever video output best suits your needs. Power up the said supergun, hit the Coin-up/Credit buttons to simulate the act of inserting a credit and press the Start button to begin an arcade game session. When you're finished, just simply power-down the supergun and respective monitor for another future gaming session.
Buying a supergun can be used as a stepping stone to graduate to the cool Japanese candy cabinets like the Taito Egret II and others. Once you get your feet wet delving into the world of arcade PCBs, it's a lifelong hobby that you'll enjoy if you grew up playing arcade games from your youth. ^_~
I suggest trying out Mame/Mame32 emulation and various arcade roms to see what would pique your interest in determining what arcade PCBs to buy if you do decide to buy a supergun setup later on.
Just out of curiosity, what are your favorite classic arcade games and/or shmup titles that you wish to play at home, Friz?
PC Engine Fan X! ^_~