C:\Users\<Your Username>\Music
and on Mac, it's:
~/Users/<Your Username>/Music
Many people forget these default folders exist, and create new local folders where they store their music. By creating a local folder, you are allocating space on your internal hard drive for your music. Wherever your computer goes, your music goes with it.
iTunes has been the frontrunner in digital music collection management for over 15 years, so we understand that many of our customers come to us from a background in iTunes.
Most iTunes collections are stored in local folders in a default location determined by iTunes, but some iTunes customers have saved space on their internal hard drives by moving their iTunes collections to non-standard locations.
We've built Roon to handle both scenarios, and you can read more about iTunes storage and how to import your iTunes library here.
A NAS is like having your own private cloud, and more powerful NAS devices can run Roon Server - a headless version of Roon. This alleviates the need to have Roon running on a laptop, Mac or PC. If Roon Server is running on a NAS device - which are typically left running 24x7 - that you use to store your music, you can simply launch a Roon control on your phone, tablet, or laptop and start listening.
To get started using music from a NAS drive, give this a read.
USB Disks are probably the most common form of storage behind local storage. They can be cheap and portable or hefty and expensive, but they're always a great way to extend disk capacity beyond the limits of an internal hard drive.
USB Disks are just as the name suggests - hard drives that attach to your computer via USB. On Windows and OS X a USB disk will show up as an ejectable drive, and they generally act the same way a local folder would.
Roon also treats USB disks very similarly to local folders, but keep in mind that there can be added instability when using a USB disk. USB ports can degrade and no longer work, wires can come loose, spinning drives can fail, etc. If your computer can't see the USB disk, then Roon won't be able to see it either. If you launch Roon and notice music missing from your collection, make sure your USB disk is running properly first!