LEDs have two legs, an anode (longer leg, positive) and a cathode (shorter leg, negative). Connect the anode to a current-limiting resistor and the other end of the resistor to the microcontroller’s output pin. Connect the cathode directly to the microcontroller’s ground (GND) pin. Interfacing an LED with an ESP8266 using the Arduino core is quite similar to the basic Arduino example. The ESP8266 Arduino core provides a convenient platform for programming ESP8266 modules with the Arduino IDE. Here’s a simple example of “interfacing an LED with an ESP8266 using an Arduino-core”ESP8266 Arduino-Core Interface – LED”: