I have a released game on Steam. I'm working on a new version, but before releasing it to the public, I want to be able to test it with my friends on Steam, through a beta channel that can be accessed through this menu:
Can I do this, and how?
From the same page you set your builds live, there's a branch list and a button to create a new branch at the top. Just press the button, create a branch, and set your beta build upload live to that branch.