Debootstrap is used to create a Debian base system from scratch, without
requiring the availability of dpkg or apt. It does this by downloading .deb
files from a mirror site, and carefully unpacking them into a directory which
can eventually be chrooted into.
It's especially useful if you need to work on debian-like systems without having
to install them over our beloved Slackware ;-)

As we do not have dpkg, remember to always pass an architecture to debootstrap
using the --arch switch.