Drivers for the Arduino clones that use the CH340 USB to Serial chip can be found below.
Install the drivers before plugging in the Arduino.
Download the drivers HERE.
Unzip it and run the installer.
Then plug in the Arduino, and it should be recognized. It may take a few minutes though.
You may need to restart the Arduino IDE to be able to select the appropriate COM port.
For OSX (Mac) and Linux, have a look at this excellent page: https://sparks.gogo.co.nz/ch340.html