For downloading Windows 8 Beta, you will have to visit windows.microsoft.com/en-US/windows-8/download. Complete information is available on the provided site which will help you in installing the Consumer Preview version.
With the tools you will have to create ISO or thumb drive.
For the ISO image use the Disk Image burner or the USB tool. This can be done from indows.microsoft.com/en-US/windows-8/iso