As you're new, here are the Forum Rules to check out. See the Wiihacks Index Page for important threads which will probably answer most of your questions.
4.2 is very hackable and as of now there is no real safe way to downgrade without having a serious chance to brick your Wii. Just follow the 4.2 guide linked in my signature below - it's current and up to date with everything you need to play backups.
If your Wii is brand new there's a strong chance it contains the D3-2 chip which prevents the drive from reading backup discs. There is no workaround yet, so you'll be limited to usb loading if this is the case.
Edit: And above all - Don't follow youtube video tutorials! Stick to this site - everything you need is here.