mrboni:
What's the hardware used?
He is using the SPI port to send data to four 8-bit shift registers: Rows, Red, Green, Blue. He sets the color bits LOW and the Row bit HIGH to turn on LEDs in a specific row. The SPI Slave Select line goes to the Latch input of the serial-in, parallel out shift registers. When the Slave Select line goes HIGH the bits that were shifted into the shift register appear on the outputs.
The circuit diagram is shown here:
http://francisshanahan.com/index.php/2009/how-to-build-a-8x8x3-led-matrix-with-pwm-using-an-arduino/