Seems as if you are new to rooting. I suggest slow down...read a little. The guide I provided you shows what "nandroid" is.
Nandroid is a folder on your sdcard.
You need to know where you are going and what you are trying to do. Make sure you have more then 50% before changing roms. Get a battery widget. Because your battery in your notification bar shows green until you are at 30%. The biggest cause of "I bricked my phone" threads are:
1) Installing Roms with low battery
2) installing Roms with out wiping data and Cache
3) Not taking the time to read and understand what is happening.