The tiny looking ESP8266 Wi-Fi Module is not just a wifi Transceiver. It Provides as much WiFi-ability as a WiFi Shield offers. It has a small Processor onboard and thus ability to work without external microcontroller.
It works with 3.3V 500MA.
Now days this cheap module($5) is popularly used in Internet of Things(IOT) projects. There are many types of ESP8266 Module available but the most popular are ESP-01 and ESP-12
You need to programme ESP8266 to do specific task for that you need one extra hardware which is CP2102 (it coverts USB data to TTL).
Wire up the Module as shown the circuit diagram below:
Steps for Programming ESP8266 Wi Fi Module using Arduino Software :
(1) Install latest arduino software (by installer only so that all driver and environment setup correctly)
(2) By default this wi fi module is not listed in the IDE so You will require to download board defination for that-> start Arduino and open Preferences window.
and paste this URL http://arduino.esp8266.com/stable/package_esp8266com_index.json
(3) Open Boards Manager from Tools > Board menu and click install esp8266 platform (and don’t forget to select your ESP8266 board from Tools > Board menu after installation).
(4) click install
(5)now using proper COM port and ESP8266 in programming(flash) mode(see circuit diagram), its ready to upload your compiled file.
The state of GPIO0 determines which mode will operate during its next power up.
GPIO0 state Operation Mode=>LOW =flash mode, HIGH or NC working mode
Now your Wi-Fi Module is ready for programme uploading.
Recommend : Now days It is advisable to use NodeMCU or Wemos . There is no much difference in cost but includes huge features. This module already includes Programming Circuit, USB communication, ESP8266 Wifi Modules and even you don’t need arduino board. It automatically changes its state from programming and operation. You can use Arduino IDE for programming.