Oscilloscopes

The Y axis is the Y gain. The X axis is the time base. 

If [3] volts are given from a dc battery and the Y gain is set to [1V/div] the dot will move [3] squares up. (This is if the time base is switched off.)

If the input is 0 volts and the timebase is switched on there is a horizontal line across the screen. 

If the input is [3] volts and the Y gain is set to [1V/div] and the timebase is set on, then the horizontal line will be [3] squares up. 

If [3] volts are given from an ac battery and the Y gain is set to [1V/div] there is a vertical line [6] squares long. (This is if the time base is switched off.)

If the input is [3] volts and the Y gain is set to [1V/div] and the time base is switched on [0.002s/div] a sine curve appears. The top of the curve will be [3] squares up and the bottom of the curve will be [3] squares down. The time period is a whole curve. If it is [8] squares long the time period will be [8] x [0.002] = [0.016s]