Before using the Mill One's cutting space, we'll need to physically prepare the machine. By milling a sacrificial piece of material, it will give the machine a 'level' bed for all your future projects to be made on.
The following video will talk about common workholding methods that you can use on your Mill One, introduce how to use Universal G-code Sender, and show you how to mill the sacrificial board. The platform leveling g-code can be downloaded here.
Note: if you have a Mac and are having issues connecting with UGS, try re-opening the Arduino IDE to see what the name of the connection to the machine is, then copy this name back into UGS and click "Open".