Several USB device examples are provided by Microchip. Some of these examples are covered by their own application note.
Basic USB knowledge is necessary to understand the USB device class application notes (Classes: HID, and CDC).
To create a USB device with one of the ASF provided classes, refer directly to the related application note for this USB class.
The new class and composite USB device application notes are designed for advanced USB developers.
Other examples are also available in Atmel Studio. To list these, select "New Example Project..." from the start screen or the File menu (File → New → Example Project...) in Atmel Studio 7. The list of examples can be reduced to list only USB by either searching for USB in the search field or select USB from the technology tab.