The easiest way would be to just print the speed out to the Serial Monitor as a start. To do that, you need to use the Serial library. There are examples in the IDE.
After you accomplish that, you will need to connect some sort of display. The easiest are the displays that use the i2c protocol (two wire or TWI) which you can purchase and install very easily. They take care of driving all the pins required to control a display. You will use commands very similar to the Serial library to write to the display, just like writing to the serial monitor.