Large Test Oscilloscope
A large classic oscilloscope at the Edison Tech Center

A voltmeter will tell you a static measurement of a circuit at one point in time. These instruments can display the change of voltage over time on a screen. The device can also record the data over time, modern oscilloscopes can drop the data into a PC for further analysis.

Further reading:
How to use an oscilloscope
Oscilloscopes for radio amateurs ARRL

Old oscilloscopes
1940s oscilloscopes on display at the Edison Tech Center

See our videos below to understand first how the screen works in an oscilloscope, and secondly where time measurement is found in the amplifier circuits.