Sorry, I am new. Do I need to buy the Single User License(mac/win) to use zbrush ? Or just to buy the Backup Disc(physical disc)?
The physical disc is simply a backup of the installer. It will not work without a license to run the software.
No matter what, you need to purchase a single-user license. You can also purchase a backup disc but that is honestly a waste due to the fact that it eventually becomes outdated (or lost) and our My Licenses page allows you to download the most current installer at any time.