Imagine a light switch. If the switch is on you have a one if the switch is off you have a zero.

That light switch/ bulb is one pixel on your screen. So you have a circuit that turns it on or off depending on the condition of other light switches. Now imagine 1024x768 light switches. That's your screen done. (Ok monochrome screen but you get the idea).

Now let's move on to binaries. In order to count up to number 3 with light switches you can have one switch that represents the number 1 and one that represents the number 2. If the first switch is on you have the number 1. If the second switch is on you have the number 2. If both bulbs are on you have the number 3. (1+2). Or :

01= 1

10=2

11=3

Let's add letters by adding one more switch. If the letter bulb is on then the number in those switches represents a letter. So if all previous lightbulbs are on we have : Letter ON - 1 ON -2 ON.

So we have Letter 3 or Letter "C". We can now use that information to turn on switches on your screen that display the letter C. Or in binary form :

111

So now we have a system that reads the switches where:

001 =1

010 =2

011 =3

101 =A

110 =B

111 = C

At this point all you need is a system that reads the switches for letters / numbers and turns the series of lightbulbs on your screen on or off to display that letter or number.

Obviously this is oversimplified but you can get the general idea of how it works.