Antenna

You can think of antenna as a black box that converts electric currents to radio waves. 

Consider a walkie talk as an example, the audio signal is converted into an electric signal this electric signal in our circuit has to some how travel through air to be received at the other end. An antenna is a transducer that converts this electric signal into radio waves.

There is so much happenign to the electrical signal inside the circuit before it reaches the antenna. If you want to practically understand what hapenns, then try building you own FM transmitter circuit like this https://circuitdigest.com/electronic-circuits/how-to-build-fm-transmitter-circuit to understad better 

Antennas are a very important component of communication systems, it transforms the RF signal, you can see the antenna in many devices like router and many more, Like I recently bought a wifi device along with antenna from Black Friday promo codes pic shown below

I hope you get to know about it.