Ground is only a connection point between all relevant components in the electronic circuit in order to make one reference point.
it is not really connected to the ground.
for example a battery with DC voltage (+ and -) connected to a voltage divider with resistors.
in order to measure the voltage on one resistor related to the battery you need to define a reference point.
you call the (-) tap of the battery a "ground" and measure all voltages related to this point (the + tap of the voltmeter connected to the measure point and the - tap connected to "ground" point)
another simple example is connecting to boards (to circuits together).
you must connect them with a reference point . you take the ground point of each circuit and connect them together.