i just installed boot mii and homebrew channel. I laso made a nand backup or what ever its called. Im using MauiFrogs guide to hack any wii. Im at the beginning of chapter 2. Do i take the sd card that i used for chapter 1 out of my wii, or do i need another one. And what will happen if i my wii gets bricked. How do i use the nand backup to unbrick it?
All the instruction you need is in the guide. You can use a different SD card if you want but that would be needless extra work when you can use the same card.
As for info about bricked Wii's, look here:
Most people will use the same SD card, after copying the NAND backup data off the SD card to the hard drive on your computer for storage, then reformatting the card, then starting with chapter 2.