This module appears to be designed for communicating with the ESP8266 ESP-01 board. The pinout for the ESP-01 is shown below, taken from a typical datasheet:
[Updated]The arrow on the CH340 board next to the yellow header indicates the connection orientation. The bulk of the ESP-01 goes on the side of the header pointed to by the arrow, covering the CH340 board, as shown below.
Information on the WCH CH340 product set including the G model is here.
There is plenty of online information on getting started with the ESP8266 ESP-01 using the Arduino IDE. A good example is at instructables.com.
The other model variations you mentioned (with built in buttons) are probably in response to a known problem with this board when flashing ESP-01s. See here for more info.