For userspace USB drivers, you want to look at libusb. I don't know of a straightforward tutorial, but the API matches up really closely to the operations you'd expect to be able to do against a USB peripheral.
For learning more about how USB itself works, I highly recommend Jan Axelson's USB Complete[1]. I used an older version of this book to build a from-scratch USB device (on an STM32F0 but not using the built-in USB example code) and libusb-based usermode driver for it.
For learning more about how USB itself works, I highly recommend Jan Axelson's USB Complete[1]. I used an older version of this book to build a from-scratch USB device (on an STM32F0 but not using the built-in USB example code) and libusb-based usermode driver for it.
[1] http://janaxelson.com/usbc.htm