OS X Yosemite will be a free download for all Mac users when it's released in the Autumn.
You can get it earlier.
As promised, Apple is throwing open the doors on the beta program for OS X Yosemite. That means anyone with a compatible Mac can download and install a preview of the software, as long as they register.
To get the preview, you'll need to sign up through the OS X Beta Program site. Once you've done that, Apple will email you instructions for downloading and installing the beta on your Mac.
Check out the video above for full details on how to get your hands on it.