Antennas take electrical power and turn it into radio waves and the other way around. These waves could be used to communicate with other electrical devices such as Arduino or Raspberry Pi to actuate something or have the microcontroller process a certain command. Of course, the uses are really limited only by your imagination. Realistically, many applications around us are done through antennas to have a less messy phsyical environment (less wires) and more modern environment. This is why mastering how to things with antennas is a must for any engineer.