Welcome to pinball ownership, Juan!
Although I’m a long time player and collector, I’ll readily admit (and my friends will eagerly confirm that I’m not really a hardware tinkerer. I’m kind of a klutz, and sort of the stereotypical software guy – fine with a keyboard, but giving me a soldering iron or screwdriver is begging for trouble.
Given that background, I feel comfortable saying: don’t worry too much about it. If I haven’t burnt down my house yet (I haven’t even burnt up a single pin!), you’re unlikely to do so. If you have experience soldering other things, those skills will transfer well to pinball machines… if you don’t have soldering experience, get some scrap parts at --Radio Shack-- errr, Fry’s? Mouser? well, somewhere, get a few wires and switches you don’t mind ruining, and practice. There are lots of good videos online to help tutor you. If you don’t have solid soldering skills, you probably want to keep the iron under the playfield, where most components are relatively large-scale, cheap parts, and not in the backbox, where it’s easier to trash a PCB with a bad soldering job. And try to keep the iron away from your body parts.
It’s pretty difficult to do any serious damage when you’re working with parts commonly found in all pinball machines: microswitches, solenoids, stuff like that. They’re relatively inexpensive and easily replaced. (One sorta-exception might be flipper adjustments: it’s possible to adjust the flipper bats low enough that they scrape the playfield surface when they move, which could wear off the playfield paint… that’s bad. But you can readily determine when this happens by sight and by feel.) You want to be more careful when working around a game’s unique components, including flat plastics, ramps, and custom devices or auxiliary PCB’s, etc. Those parts can be difficult to nigh-impossible to replace, and accordingly expensive if you do find replacements.
And as Williams suggests, look around the Web for guides… there’s LOTS of great information out there. And feel free to ask here… whatever problem you’re having, surely several other people have also had.
BTW, earlier I mentioned my dubious skill set, but even so, I’m able to do stuff like tear down and rebuild playfields (for cleaning, replacing ramps, etc), solder loose playfield wires, adjust switches, rebuild flippers, etc. If I can do those things, anyone can. I keep the heck away from PCB repairs, and am thankful to have a good friend who donates his time to deal with those when needed (thankfully, not too often!).