Handbook:Parts/Installation/Bootloader

Rebooting the system
Exit the chrooted environment and unmount all mounted partitions. Then type in that one magical command that initiates the final, true test:.

Of course, don't forget to remove the bootable CD, otherwise the CD might be booted again instead of the new Gentoo system.

Once rebooted in the freshly installed Gentoo environment, finish up with Finalizing the Gentoo installation.