When installing a gentoo system for the first time, please refer to the wonderfull [gentoo handbook](https://wiki.gentoo.org/wiki/Handbook:AMD64). This page is just installation notes shorthand when you know exactly what you are doing.
You can get a bootable iso or liveusb from https://www.gentoo.org/downloads/. I recommend the minimal one. To create a bootable usb drive juste use `dd` to copy the image on it. Then boot on this brand new installation media.
Once you boot on the installation media, you can start sshd and set a temporary password and proceed with the installation more confortably from another machine :
There are several options depending on wether you need soft raid, full disk encryption or a simple root device with no additional complications. It will also differ if you are using a virtual machine or a physical one.
Make sure you do not repeat the mistake I too often make by mounting something to /mnt while using the liveusb/livecd. You will lose your shell if you do this and will need to reboot!
Get the stage 3 installation file from https://www.gentoo.org/downloads/. I personnaly use the non-multilib one from the advanced choices, since I am no longer using and 32bits software except steam, and I use steam from a multilib chroot.
Put the archive on the server in /mnt/gentoo (you can simply wget it from there), then extract it :
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tar xpf stage3-*.tar.xz --xattrs-include='*.*' --numeric-owner
mount -o loop,noatime,nodev /portage.img /usr/portage/
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We set default compilation options and flags. If you are not me and cannot rsync this location, you can browse it from https://packages.adyxax.org/x86-64/etc/portage/ :
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rsync -a --delete packages.adyxax.org:/srv/gentoo-builder/x86-64/etc/portage/ /etc/portage/
sed -i /etc/portage/make.conf -e s/buildpkg/getbinpkg/