Plug your USB drive into Mac OS X, and open Disk Utility (located in the Utilities folder in the Applications folder).
Select the USB drive in the sidebar of Disk Utility, go to the "Partition" tab of Disk Utility.
You'll have to erase that hard drive with Disk Utility first (check out Step 4 of our Snow Leopard installation guide for more details). Select it (use the arrow keys on your computer) and press "Enter".
Otherwise, select the hard drive you want to install OS X Mavericks on, and click "Install". Once again, if you get a kernel panic/loading error when you try to boot your new Mavericks installation (or if the installation simply won't start within 10 minutes), you'll need to enter some boot flags.
Choose the "Mac App Store Mavericks - 10.9" option.
In addition, there are two extra options you might want to select: "Legacy USB Support" and "Laptop Support".
Then, once you've booted back into the Unibeast menu, try type any necessary boot flags before pressing the enter/return key.
Multibeast is a collection of kext files that you'll need to install for your Hackintoshes to have sound, internet, a high resolution screen, and more.
If you're installing Mavericks on an empty hard drive, the hard drive selection box will be blank. If your Hackintosh already had Mac OS X Snow Leopard, Lion, or Mountain Lion installed beforehand, you can unplug the Unibeast USB drive. At the boot screen, you'll see an icon for the hard drive where you installed Mavericks.
If things go well, your computer will boot from the USB drive instead of booting from your normal hard disk. If you do not manage to reach the Unibeast menu, check your motherboard's BIOS settings to make sure that the changes you made in Step 4 were properly applied.
If they were, but you still cannot boot from the Unibeast USB drive, unplug your USB drive, and go back to Step 1.
If your Hackintosh doesn't have any version of Mac OS X installed yet, you have to change a few extra BIOS settings.
Before starting, reset all of your BIOS settings to their factory defaults.