It is a small device that looks like a memory stick. It plugs in to a USB and provides WiFi to devices that aren’t WiFi enabled, such as older desktop computers
Mine was a tiny thing that plugs into a USB socket on my PC and enables my pc to connect via wifi with my router. It was a bit too tiny to do a good job, so I bought a bigger one (which had a six inch aerial attached) and that works fine. I need a dongle because my PC doesn't have built-in wifi capability. My big dongle cost about £15.
The dongle will allow you to connect to free Wi-Fi in a coffee shop, hotel, fast food outlet etc
In addition, there is a very good chance of connecting to the internet via a hotspot if you find yourself in a remote countryside location. T
Albeit the dongle being a very handy accessory, may I suggest if your PC does not have built in WI-FI, perhaps now is the time to be thinking about updating your computer.