The SPI Bus - Exploring Arduino: Tools and Techniques for Engineering Wizardry - page 191

Figure 9-6: Potentiometer LED setup
The code in Listing 9-1 executes all these steps and includes a function for
passing the SS pin, register byte, and command to a given chip via SPI. The SPI
.begin() command enables you to initialize the SPI interface on the hardware
SPI pins of the Arduino, and you can use SPI.transfer() to actually send data
over the SPI bus.