Huh?
The A520 (
http://www.amiga-hardware.com/showhardware.cgi?HARDID=725) is a RF-modulator (and also provides Composite Video output) primarily meant for the A500, but also works on any other Amiga. Won't do you any good on it's own, so I'll assume you also brought an A500 down from the attic.
The switch that runs to the trapdoor is most likely a switch to enable/disable a RAM expansion card (usually 512kB, but larger expansions are also around). The purpose of disabling the RAM expansion is for compatibility with a few games that can't handle anything more than the A500s built-in RAM.
As for Workbench, this is not required for playing games, just stick any game disk in the drive and the game will boot. The files you found on the net would AFAIK technically be piracy, and the only option that is 100% legal is to actually buy a set of disks from someone. (but you'll probably find I kind soul living in your area/country willing to mail you a set for the cost of the disks and postage).
-Paul