An oscilloscope is a powerful diagnostic tool allowing a direct connection to sensors out put going way beyond what live data from a scan tool is capable of telling you
Basically an oscilloscope is a graphing volt meter,or volts over time.
Voltage readings and time in numerical form are not easy to interpret the other dimension that an oscilloscope gives is frequency.
I change per second is 1 hertz and then on up to giga hertz .
Voltage changes from an engines sensors alter over a time period of milliseconds that a digital voltmeter stands no chance of displaying