If you want to play with some LED matrix displays Nuxie1 has written a guide to help you get started.

“An LED Matrix is an array of LED’s with the anode or positive terminal of each row connected together, and the cathode or negative terminal of each column connected together. Or the anode can be connected to a column, and cathode connected to a row.

Using just a microcontroller with a 5×5 display would require 10 available output pins on the microcontroller. Also, the output pins would have to be capable of sourcing and sinking the required current to drive it. As a worst case scenario with all LED’s on and drawing 5mA, the microcontroller would have to source 25mA in total (since only one row or column would be on at one time).”