First, install eselect-repository package if it isn't installed on your system:
$ sudo emerge --ask app-eselect/eselect-repository
Next, use eselect repository command to add a local repository named an9wer, whose path points to the subdirectory gentoo in this repo:
$ sudo eselect repository create an9wer /path/to/pkg/gentoo
Finally, install some Gentoo package in this repo as follows:
$ sudo emerge --ask x11-wm/dwm::an9wer