It's simple school maths!.
An oscilloscope is nothing more than a piece of graph paper!.
It displays a graph of voltage (y axix) against time (x axis).
The y axis is calibrated it volts per division, and can be read from the input attenuator control, and the x axis is in milliseconds per division, and can be read from the timebase control. Obviously different settings of the controls move from volts to millivolts, and from milliseconds to microseconds etc.
You should have learnt to read (and draw) a graph at school, reading a scope is not really any different.