Despite some of the listing titles calling it a shield, that is not a shield. It's a standalone board. A shield is a circuit board with some circuitry on it that can be plugged into an Arduino board to give it new capabilities. The shields have male pins on the bottom that match the female headers on the Arduino so it plugs right in. The WeMost D1 R2 is a ESP8266 based board in an Arduino Uno form factor.
One thing you need to keep in mind with this board is that it uses 3.3 V logic levels rather than the 5 V logic levels of the Uno and other common Arduino AVR boards. Most 5 V devices can interface with a 3.3 V input correctly. There is some concern about sending 5 V signals to the inputs of the 3.3 V ESP8266. There is some evidence that it may be 5 V tolerant but I don't consider it to be conclusive. It's fairly easy to shift the voltage levels.
Another thing to consider when directly programming the ESP8266 is that some of the popular libraries or example codes are written specifically for the more common AVR architecture and will not work on ESP8266. There is fairly good support for ESP8266 but you may want to check that any code you're planning to use with that board is compatible.