ESP8266 was initially intended as a serial port to wifi bridge, but can also be used as standalone microcontroller. There is even support for Arduino IDE.
In order to get used to the ESP8266, it is a good idea to get a development board. These boards contain a pre-soldered ESP8266, access to the GPIO pins and usually a USB connector which can be used to communicate with the ESP8266 and supply it with power.
Wemos D1 Mini
It uses a CH340 USB serial converter.
Bootup GPIO state
- AT firmware, turning the ESP8266 into a serial/wifi bridge
- NodeMCU firmware, allowing Lua programming
- Arduino port (documentation), using the popular Arduino/C programming language
- MicroPython firmware
- Basic firmware
- ESPlorer integrated development environment mostly useful for AT, Lua and MicroPython development
- Arduino integrated development environment
- ESPtool Python package
If you just need a superfast cheap microcontroller without wifi, check out nodsk8266.