Heads is supported on a limited set of hardware (laptop and security dongle). First, check the Prerequisites page for details.
You can download ROMs directly from CircleCI for most of the boards configurations supported.
If you are building heads check the build guides. See below if you are using heads releases from this project.
The steps for Flashing-Guides on your system may vary based on the hardware in use.
There are many secret pins, passphrases, and keys used in heads. These are described in Configuring Keys.
We assume you want to run something other than heads on your system. The installation procedure could vary greatly depending on which distro you choose, which version of that distro, and if you are encrypting various partitions. See Operating System for help.
There is a Recovery Shell built into the heads environment which may be used for troubleshooting.