That's about a succinct and answer as we can expect ... from someone who knows nothing about computer technology.<quoted text>
The computer uses binary codes, duh
Did you know that every single pixel, that's what the little colored dots on your monitor are called, is actually a number? Well, three numbers, technically four but the fourth is not used unless you have it set to utilize the extra data, but then you have to have a faster processor as it has to bit align the data or all you get is garbage, then you need a graphics card capable of matching that setting as well, or it will realign the bits and all that effort is wasted. Most images stored in data formats are 32 bit, or 64 bit but I don't see why people are so excited about that extra data being used since our eyes cannot detect the difference at a reasonable distance of viewing. Each number, typically 32 bits of data lumped together sequentially into a byte, represent intensities of color, by varying the three primary colors of red, green, and blue, you can create almost any color, I say almost because being binary limits the values between 1 and 0, full on and full off. The fourth value is often used as the alpha channel for data format images, the alpha channel is "how much" to mix that color with the color it's being put over, but only the png format utilizes this to the fullest potential, others will just be one or off like the gif format.
.... and that's just a tiny, very tiny, bit of information on how a computer works now. So tiny it would take a million of these posts just to explain the very basics.