Today's world is full of devices that transmit data wirelessly. Wireless transmission is convenient for the receiver of data because you don't need to be connected to a wire to receive data. It's convenient to the sender of data because it reduces clutter of many wires and the cost of construction of cable lines.
Data can be transmitted over the air using energy waves. Energy comes in all sorts of frequencies. A frequency is how many times a wave goes up and down in a second. Energy waves tranveling at frequencies between 7 kHz (7,000 cycles per second) and 300 GHz (300 billions cycles per second), are called radio waves. When people discovered radio waves coming from space along with visible light, they started experimenting with using these waves to send energy around the Earth.
Radio transmission requires two parts. A transmitter to create the wave. And a receiver to decode the wave.
Energy can be created by attaching a battery to a wire. When both of the ends of the wire are connected to the battery's plus and minus terminals, the battery sends a flow of electrons through the wire. This creates energy flow.
An energy wave can be created by connecting and disconnecting the battery repeatedly. This would create the simplest energy wave, called the square wave.
The smoothest type of wave good for sending data is a sine wave. A sine wave can be created by connecting a wire to a capacitor and an inductor.
A simple sine wave has uniform waves all throughout. By changing the height of those waves or the distance between waves, you can encode data into the wave. Much like you could encode entire text messages with just dashes and dots of Morse code.
The job of the transmitter is to encode data into a sine wave, and to send it in all directions for anybody who would want to listen.
The job of the receiver is to listen to a particular type of wave, and decode it into sound, image, and video, which people can hear and see.
Millions of devices in your city, encode audio and visual data and send it out into space in all directions. These waves travel through us all the time, but we don't see them. With the help of different devices with built in receivers, we are able to decode the information sent, to see it and hear it.
Sources:
"How Radio Works - HowStuffWorks." HowStuffWorks. N.p., n.d. Web. 03 Nov. 2014.