Create an instance of it, like MCP4151 pot(CS, MOSI, MISO, SCK).
Where CS is chip select pin, MOSI is the output on the Arduino, MISO is the input, and SCK is the clock.
On the MCP4151, the MISO and MOSI are on the same pin. Use a 1 kOhm resistor to pull down the MISO pin
on the chip to GND, with the MOSI line (on the MOSI pin of the Arduino) in series with the resistor. There's another constructor that accepts more parameters if one needs more customization.

Import it into your project with #include <MCP4151.h>.

pot.writeValue() and pot.getCurValue() where 'pot' is the name of the object initialized.
Function pot.getCurValue() retrieves the stored wiper value from the chip. If this isn't needed,
then connecting the resistor and MISO line are not needed and the Arduino can just have its MOSI line
connected to the chip's pin 3.