gentoolkit:
http://www.gentoo.org/doc/en/gentoolkit.xml
USE flags:
http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=2
Portage:
http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=1
install-zh:
http://gentoo.linuxsir.org/doc/zh_cn/handbook/handbook-x86.xml?style=printable&full=1