Hacking I'm a little confused.

[snuffychris605]

So ever since a few youtubers started posting videos with modded skins and using WiFi, I was wondering how I could do that myself. What files should I download first? Im really only in to add skins that I wanted in smash, but did not make it, like Dark Bowser. I've done Homebrew on a Wii before, but this is a whole other way that I don't really understand.