Getting Started with ESP8266:
The ESP8266 is a low-cost Wi-Fi module, in which we can connect the wifi, it can run as a server or a client according to the programmer or user.
Comparing ESP8266 with other wifi solutions, ESP8266 is the best option for “The Internet of Things”. There are so many resources and it is low in price.
Versions of ESP8266:
There are totally 16 versions or variants of ESP8266.
Mostly used are ESP-01 or ESP-12E NodeMCU Kit or Wemos-D1 Mini. For comparison of these 3 refer to this link.
The successor of ESP8266 is ESP32. The ESP32 consists of dual core-CPU, both wifi and bluetooth, more no. of GPIO pins compared to ESP8266.
Features of ESP8266(ESP-01):
●Frequency upto 52MHz
●1MB Flash memory
●Used as a client or server.
●Programmed through Arduino IDE or Lua Script.
Pin Number    Pin Name     Function Alternate Function
1     Ground     Connects to the ground of the circuit. -
2     TX     Transmits the data. Can be used also GPIO-1.
3     GPIO-2     General purpose input/output-2nd pin. -
4     CH_EN     Chip Enable - Active High. -
5     GPIO-0    General purpose input/output-0th pin. When this GPIO is connected to GND we can download/update our firmware.
6     Reset     Reset the module. -
7     RX     Receives the data. Can be used also GPIO-3.
8     Vcc     Should connect to power supply of 3.3V. -