LibraryBox v2.0 is a combination of a router (a variety of hardware will work), USB drive, and software that, when combined, give you a small, low powered webserver. The webserver acts like a captive portal, and delivers files that are stored on the USB drive.
To use LibraryBox, you simply connect to the wifi SSID "LibraryBox" and launch a browser. Attempting to visit any webpage will push you to the LibraryBox homepage on the device, which has information about the project, and links on the menu for downloads. You can browse the contents of the Shared folder, and download any files you'd like. The device you are using does have to be able to understand the download (for instance, downloading an EPUB ebook to a Kindle won't really work).