The digital signal doesn't want to represent analog signal as "squared things", so when you see a 1 in a digital signal its not equivalent to a high amplitude in the anlog singal, but it wants to represent the height of the amplitude to different times as a number (but in binary format). So many binary numbers want to represent the height of the amplitude to one specific time.
Consider this picture from BBC:
The above graph is the analog form.
From that, a value is taken each second (but this can go up to 40mio. times a second and much much more). This value is the amplitude height of the analog signal.
Lets call it "step" when we take the value.
In each step, the height of the amplitude is recorded. The height is a number, which can be represented as 0 and 1 (for instance 10 would be 1010).
You see, the more values we measure each second, the more data has to be saved/transmitted and the more accurate the resulting digital format of this analog signal will be.
Also, the higher the value can be, the more accurate the resulting digital format will be too. (for instance when we take values from 0 to 10, there are only 10 values - not very accurate. When we would remodulate this digital signal into an analog one, the curve wouldn't be very "good". But when we take values from 0 to 16000, this will be a lot more accurate.) Also more bits have to be saved here each step.
If you save 64Bit each step and the step is made once a second, you save 64Bit/s.
If you save 32Bit each step and the step is made twice a second, you save 64Bit/s too.
If you save 16Bit each step and the step is made 4 times a second, you have also 64Bit/s.
There are many ways to convey a digital signal.
For example by "changing voltage" which is called "Amplitude Modulation", which is shown in you graph (but of course its NEVER a perfect square!). Amplitude Modulation just means that you singal that there is a 1 by a high amplitude (high voltage) and a 0 by a low one.
There are oder modulation techniques like Frequence Modulation (FM which is used with radios - you indicate a 1 with a high frequency and a 0 with a low one) or Pulse Amplitude Modulation which is used in Ethernet and many many more!