How does a computer translate 0s and 1's into things like letters and pictures?

A digital computer uses binary (base 2) to store numbers. Binary numbers only have two states 1 and 0.

Humans count in base ten because we have ten fingers.

We learned to count by using our fingers to count from 0 to 9. When we got this far we ran out of fingers so we took a stone or made a mark and said that that equalled ten then reset our fingers to zero and counted over adding the value of the mark to the value on our fingers.

So imagine if we were an alien and only had one finger? How would we count? well probably the same way. We would count zero, then one, then we would draw a one and reset out fingers back to zero. if we look at this we have;

00 Base 2 = 0 base 10

01 Base 2 = 1 base 10

10 Base 2 = 2 base 10

When we add one by counting our finger plus the mark representing 2 (base 10) we get;

11 Base 2 which equals 3 base 10.

So in essence when we get to one number below the value of the base system we are counting in we do a 'rollover' and increment the next column and reset the previous column. Using this theory we can count in any base.

The computer only has the ability to store 2 values, these are one and zero. Essentially the computer has the same as our alien, just one finger. So it can only count in binary.

But this isn't a limitation as any base ten number can be represented in base 2. moreover the computer can use a number to represent a letter number or any keyboard symbol. When you press a key the computer stores a value in binary which represents that key.

That number is then looked up in a table which contains the graphic information for the letter and that graphic is printed to the screen at the current cursor point.

The graphic which makes up the letter is a series of numbers too! In this case each number represents the colour of a point (or pixel) in the letter graphic.

Generally three pieces of information are required to light a pixel on the screen a red value a green value and a blue value. The bigger these three values are the more variations of colours are available. These values are scanned by the video card in its ram and sent to the monitor.

Everything you see on a screen display is generated this way. It's all numbers.