The ESP8266 comes with two LEDs: one that's red, and another that's blue. Both of these LEDs can be controlled from the scripts you load on the board. This recipe will show you how you can control each one, and will end with an animation that blinks the lights between red and blue.
The techniques that are shown in this recipe can be used in your own projects whenever you want to signal some sort of status to your users. You might want to have a blinking blue light when you are scanning for a Wi-Fi network, or to light up the red light when your board has lost its network connectivity.