Gentoo is a source distribution, very efficient and well done, with a very good documentation and community.
If you want to do something with gentoo (configure sound, install X, etc), first try the official howtos of gentoo, and on the gentoo wiki, by typing “gentoo <thing> howto” in google (or “gentoo guide <chose>” for French documentation). There are really a lot of howtos.
Chrooting is a well-known procedure for Gentoo users because it is necessary for its installation, and it probably works with other distributions but I'm not sure it is the same syntax.
Chrooting consists to “change root”, to run a system you have not booted on (for example you boot on a live cd, and you chroot to your system and you can run
emerge etc on your system).
If your system is on hda5 with a reiserfs file system, do once:
mount -t reiserfs /dev/hda5 /mnt/gentoo cp -L /etc/resolv.conf /mnt/gentoo/etc/ mount -t proc none /mnt/gentoo/proc mount -o bind /dev /mnt/gentoo/dev
And for every shell you want to open:
chroot /mnt/gentoo env-update source /etc/profile