Method #2: The Advanced, Flexible Way

If you're feeling more adventurous (or want to minimize how much you have to download directly from Steam), you can use the secondary method. There are two primary differences between this method and the previous one. For starters, the download is significantly smaller. Part of the reason for this is because once you install the OS, you still need to download Steam. What you're installing is mostly just a customized version of Debian. More importantly, though, this method has an Expert Install mode. You can use this method to tweak a few settings. That being said, if you're not extremely experienced with Linux distributions and installs, you probably shouldn't mess with this. To install SteamOS via this method, follow these steps: Unzip the smaller, SteamOSInstaller.zip file to your USB stick. Boot your machine from the USB stick. Select the UEFI entry from the boot menu. Select "Automated Install." Once the install is finished, boot into the OS. You will be faced with a login screen. There is a default account with both the username and password are "steam". Log in with these credentials. Double-click the Steam icon on the desktop to download and install Steam. After this, you can log in to SteamOS via the login menu you used in step 5 (select "SteamOS" via the dropdown box) with the same credentials. If you'd like to maintain the Debian installation and log in to SteamOS only when you need it, you can simply end here. However, if you'd like to commit all the way, follow Valve's instructions here from step 8 in the final section onward to make the final customization tweaks so that the partition is 100% Steam.