emerge layman

(for layman 1.1)
# echo "source /usr/portage/local/layman/make.conf" >> /etc/make.conf

(for layman 1.2)
# echo "source /usr/local/portage/layman/make.conf" >> /etc/make.conf

(for layman 1.3 and later)
# echo "source /var/lib/layman/make.conf" >> /etc/make.conf

layman -L

layman -a <overlay-name>

emerge -av <category>/<package>

layman -S