A 20MHz oscilloscope is a basic electronic measurement instrument capable of displaying and analysing signals up to 20 million cycles per second.
Oscilloscopes measures voltage over time and allows you to visualise and analyse the electrical signals in a circuit. The oscilloscope displays these signals as waveforms on its screen, showing how the voltage of the signal changes over time.
While a 20MHz oscilloscope is a good starting point for many applications, it might not be suitable for high-frequency circuits or complex signal analysis. For those tasks, higher bandwidth oscilloscopes are required.