When you have circuits that have constant voltages a multimeter is a tool that can be used to measure a single number for the voltage. This becomes redundant when you start building more complex circuits. This is where an oscilloscope comes in handy.
An oscilloscope allows you to view how voltage changes over time. These voltages are called signals which are used to convey information such as an audio signal playing music on a loudspeaker.
Some of the things that the display screen on an oscilloscope shows is the measured signal of the voltage using a graph. The voltage is represented on the vertical axis and time on the horizontal axis.
This display will allow you to determine if the behavior of your circuits is working correctly. It will also allow you to locate any problems within your circuit like unwanted signals called noise.
There are two types of oscilloscope; analog and digital. More on that later, because now we will cover a brief history of the oscilloscope.