Pachinko is pretty odd to describe. So for the sake of trying to explain it, I'll just say it's like Pinball: with 150% more lights, more noise and a reliance on sheer luck. You pop some balls into the machine and watch them drop. I don't think there's much more to it than that to be honest.
Only the brave wander into Pachinko parlors. Along with the Pachinkoholics, the chain smokers and the jobless. Walking into a Pachinko parlor will garner some dirty, un-welcomed stares. The Pachinko veterans can sniff a newbie a mile away, and they will take a minute out of their game to stare you and up an down and then shuffle their trays of Pachinko balls closer to them as you walk past. You trust NO ONE in a Pachinko parlor. Every body is the enemy. Aside from the Pachinko veterans, you also have to contend with the cacophony of noise that greets you when you walk into a parlor. I damn near went deaf. It's easy to look down on those who seem to make a career out of playing Pachinko. But I have to applaud them. They should get medals for being able to deal with the noise, the smoke ridden air and the lights for hours on end. Although they'd probably trade the medal in for some pachinko balls.
I'm a mean bastard, so I recommend that you go check out some Pachinko parlours when you're in Japan. And also visit Nagoya - which is the home of Pachinko.