This is a brief tutorial project showing a basic multiplexed LED display by BareBones3d

Due to the fact that microprocessors compute very quickly, and the human eye has persistence of vision, where an image that is seen remains visible momentary even after the image has disappeared, it is possible to flash LED's very rapidly to produce the effect that they are on simultaneously even though they are not.  This technique can allow less pins to be used on a microprocessor to drive a greater number of LED's than would otherwise be possible if each LED had to be controlled by it's own individual pin.  This process is called Multiplexing, and this tutorial will show you how to set up an LED multiplexing circuit.