Most people will download roms, which is technically illegal although with 30 year old games there usually isn’t much concern on enforcement (heck, even Switch games aren’t really enforced). The legal way is to dump the rom from the original cartridge, though, and there are tools for that. Honestly, as long as you own the original game I’m pretty sure you can just argue you have a license to play, though.
Generally you can’t share links to roms on communities, although I bet some communities are cool with it (/0 maybe?). Try not to go anywhere that looks suspicious, in any case. Most people don’t malware Gameboy games, though lol. They won’t be .exe in any case.
As for getting it to work, Android and iPhone have different emulator apps available on their respective stores. I tried MyBoy prior but tend to prefer Retroarch (which covers multiple systems, but is a like harder to setup). On Mobile, default has controls on screen so it’s pretty much plug and play though. It’s so much more convenient than digging up ancient systems, though!
Japan uses weaker voltage and many things don’t require a ground or can rely on an alternative method. That said, they’ll have a good ol’ three prong for appliances and newer buildings will have a few three prongs in select locations.