is there book which explains LFS?
 

e.x. why should we build glibc and many times?

is there any book which explains every step in detail ?

thanks!

did you read the LFS book?? it explains why glibc, binutils, and gcc needs to be rebuilt more than once--

http://www.linuxfromscratch.org/lfs/view/stable/

thanks

yes, I read it, but still I can not understand it.

Then perhaps you're not ready for it yet?

How long have you been using:

• GNU/Linux?
• Any unix?

Have you tried any other distros?

Linux from scratch is being build with a toolchain, a toolchain is a set of tools, like gcc and binutils, then you if you have a toolchain then you have them to build again with the toolchain.
thats why the directory is called tools, it's simple.