This is a Popular and Simple LED Flasher circuit using one 555 timer ic and some other components.
This circuit works on the principle of Astable Mode operation of 555 timer. Which produce a continuous Pulse wave at output on pin 3. When pulse signal is High then one connection of LED get positive supply through pin 3. and then again when Low output pulse produce then the negative supply goes to second connection of LED .
When negative supply given through pin 3 then the LED get positive supply through directly vcc. And When positive supply given by pin no 3 then negative supply get from directly negative supply of battery. Therefore both LED connection get continuous a positive and negative supply and Flashing according to output of pin 3.
The speed can changed by moving the preset R1 or changing the capacitor value of c1.
You can arrange the LEDs as your own choices with different patterns.You can operate 10-12 LEDs easily without any issue with this circuit.