Hi Annna,
The foremost book on the subject is still Jan Axelson's book:
USB Complete: The Developer's Guide (Complete Guides series)
There are other published texts on the subject, however the list is unfortunately very short and Jan's book stands far above the other few.
Developing a USB device can be extremely difficult to rather painless depending the protocol model being implemented.
As JoseMiguel recommended, the best approach maybe to purchase a development board which is well documented and supported.
I have at least one of each of the following:
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The first three choices are the least expensive $40-$60 USD and most likely the best choices for the novice. The second and third items are PIMs which you can plug into an PIC18 Explorer board in the future.
Also be sure and download/read the user manuals, guides and other docs pertaining to USB on the product pages above, they contain a wealth of information concerning USB development.
I also have the:
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It's an inexpensive kit, however to debug an app requires purchasing additional accessories. I believe one of the two PIMs I list above to be a better choice.
I prefer Microchip's Dev Boards for the development of commercial applications, they are extremely well documented, supported and large user base.
However if you desire a board for educational purposes only, you might take a look at MikroE's
EasyPIC6 Development System
This latest dev board has a Microchip ICD port making it compatible with MPLAB and supported compilers, earlier versions require the use of MikroE's compilers and IDE, unless you want to do some fancy footwork. Personally, I find their boards way too cluttered to do commercial development, but they do offer a lot of bang for the buck for students.
Checkout the following for more info on the USB Protocol:
Embedded USB - a brief tutorial
USB interface tutorial covering basic fundamentals
Hope the info helps in your endeavors.