If you want install Oracle Linux on Oracle VirtualBox, you can follow this guide to download the VM tool, ISO file, and create the VM.

To begin with, it's definitely not easy to install SteamOS in VirtualBox. Valve clearly didn't intend for you to do this; you can't just mount an ISO and install it, like a normal Linux distro.

Installing Debian Linux on Oracle VirtualBox A few months back, I posted an article about setting up a small home server.