When you connect the WeMOS D1 mini board for the first time on your Windows computer through a USB cable, it might be the case to install a USB-to-SERIAL driver. The board has a USB-to-SERIAL converter (CH340 chip). The driver is
WeMos D1 mini pins and diagram
Diagram Pin Pin Function ESP-8266 Pin TX TXD TXD RX RXD RXD A0 Analog input, max 3.3V input A0 D0 IO GPIO16 D1 IO, SCL GPIO5 D2 IO, SDA GPIO4 D3 IO,10k Pull-up GPIO0 D4 IO, 10k pull-up, BUILTIN_LED GPIO2