ESP-01 ESP8266 Module Wireless
Wi-Fi module through which your projects (developed with Arduino or any other microcontroller with UART device) can access the Internet wirelessly and transmit / receive data.
The module uses the SoC ESP8266 which presents all the hardware and software resources for your internet connection. Implements inside the stack of TCP-IP and UDP protocols, so it is not Arduino (or microcontroller used) which has to manage Internet protocols and allows, using an AT command set to request / send an HTTP page, file, or other resource or use your own arduino as a server.
On the web trovere numerous tutorial to use it better, but also the same instructions to update the firmware of the module, which is located in the non-volatile external memory.
This module requires a power supply 3.3 volts. It does not tolerate 5V power supplies. Connect RX or TX to Arduino 5V may damage it. You must use a logic level converter and a regulator to 3.3V.
The power supply of 3.3V Arduino Uno is no good because it does not supply sufficient energy to power this module. You must provide a separate 3.3V power supply, capable of delivering at least 300mA.