I'm not sure which videos you're talking about, but getting emulators for those two systems is pretty simple. Especially when compared to setting up something like a PS1 emulator.
The first thing you need to do is get the emulators. You can find Mojo GBA on the market. There is a free and paid version but I think the paid version only removes ads, you can still play/save/load with the free version. Then the only N64 emulator I've used (because it works great) is N64oid. I'm not 100% sure, but I think it was removed from the market so you'll need to find it on the web and download it. There might be alternatives to it on the market, I dunno.
After you have those you go ahead and find and download the games (roms) online. We can't link you to them here because it's against the rules I believe. Then locate the games in the emulator and play them. Sometimes certain games don't run well in certain emulators, but the majority of games should work.
