First and foremost, building Linux is going to take you using the shell a lot. If you aren't comfortable using a bash shell and the "make" utility to build software, you'll want to check out these links first (this list is in the book in the "Prerequisites" section of the Foreword)

http://www.tldp.org/HOWTO/Software-Building-HOWTO.html

http://www.linuxhq.com/guides/LUG/guide.html

http://hints.cross-lfs.org/index.php/Essential_Prereading

Most of the things you'll be doing are completely safe and can be performed as an ordinary user. You will probably want access to your computer's administrator account even though it's not completely necessary, though. This is because I will assume that you are installing some tools directly to your host operating system. You can build a useful linux system completely this way, provided you're okay with not being able to boot into it. However, if you want a bootable operating system, some disk and hardware configuration are necessary, and any time disk or hardware configuration is performed there is some risk of damaging or destroying both data and your host operating system. In this case, you are going to need both administrative rights to your computer, and you are going to want to back up any important files and keep a recovery disk handy.

I will be sure to warn you before any potentially dangerous steps are performed. In the video in the "File System" section in this task, there is a single dangerous command at the end of the video.