Basically, an oscilloscope shows you a snap shot of a signal in a short time. The horizontal and vertical axis are divided into grids or divisions. There is usually 10 divisions for both axis. The horizontal axis is the time, and it is given in time/div.
Let's say you adjust the time base on the scope to 10 milliSec/div. That means that every horizontal division shows you a 10 milliSec time snap shot. Since there is 10 divisions, the total snap shot on the screen is 10 div * 10milliSec/div = 100 milliSecs. That means you are looking at a 100 milliSecs snap shot from left to right.
The vertical axis is the
voltage and it is given in volts/div. If it is set to 10 mV/div, that means every vertical division is 10 mV/div, and since there is 10 vertical divisions, the total voltage as displayed on the screen is 10 div * 10mV/div = 100 mV from top to bottom.
That way, using the scope, you can view a snap shot of how a high frequency waveform behaves, and measure its frequency, and amplitude.