There are currently two bootable media images available for download on https://www.gentoo.org : the minimal installation CD and the admin CD. These image files may be written to media in order to boot a physical machine, or used to boot a virtual machine.
The bootable media can be used to installl Gentoo, though for more complex needs, other Linux distributions may be more appropriate to conduct the installation from.
Minimal Installation CD
The minimal Installation CD provides a very light environment which may be used for Gentoo installation. Note that the emerge command is not available.
The downloaded file will have a name along the lines install-amd64-minimal-20220130T170547Z.iso.
The admin CD contains a few extra tools than the minimal installation CD but remains a very light media.