Using unRAID is the "best" way, probably not the only way. As far installing it goes, all you need to do is extract the unRAID files onto your usb and boot off it on any machine . It is easiest thing in the world. For another way, refer to this post on Wiki. It does mention a way to do it in Windows but that link is dead. Haven't looked hard to find it again.
To use a registered copy of unRAID, whether the Plus or Pro version, the flash drive must have a valid GUID. A GUID is like a product serial number, but does not actually exist on the flash drive. It is constructed by the Linux kernel from the flash drive's manufacturer, product ID, and internal serial number. The foolproof way to check if your device has a usable GUID, is to download the UnRAID software, extract it to your flash drive (USB Flash Drive Preparation), boot unRAID in a test machine, go to the Web Management page (top of the UnRAID Manual), and just select/copy/paste the GUID from the Devices tab. If the last 12 characters of your Flash GUID are all zeros, then it does **not** have a serial number and you can **not** register it. You can also utilize a Microsoft utility UVCView.mspx from within Windows to determine the USB device's GUID (which consists of idVendor+idProduct+0000+iSerialNumber), but this is unofficial, and should not be used for registration.