This circuit will flash the led on and of at regular intervals.
How it works:
From left to right, the two resistors and the capacitor set the time it takes to turn the led on or off, by changing the time it takes to charge the capacitor to trigger the timer. Next is the 555 timer, this is where all the work gets done to determine the time the led stays on and off. It contains a complicated circuit inside, but since it is packaged in the IC it can be used as a simple component.The two capacitors that are right of the timer are just accessories so to speak, but are needed for the timer to work correctly. The last part is the resistor and the led, the resistor is there to limit the current on the led so that it won't burn.