Okay kid, so you know how sometimes you like to color with crayons? Well, imagine you have four different crayons - one is for making things blue, one for making things yellow, one for making things magenta (which is kind of like a mix of purple and pink), and one for making things black (which is really dark).
Now, let's say you want to color a picture of a big yellow sun in a blue sky with some pink flowers on the ground. You can use your crayons to draw all those things, but if you want to be really detailed and make sure everything looks just right, you might want to use something called the CMYK color model.
CMYK stands for cyan (which is kind of like blue-green), magenta (remember that one?), yellow, and key (which means black). These four colors are used by printers to create all the different colors you see in a printed image.
So, instead of just using your yellow and blue crayons to make the sun and sky, you could mix cyan and magenta together to make a shade of blue that's just right. And instead of using your pink crayon for the flowers, you could mix magenta and yellow to make a more vibrant pink color. And if you need to make something really dark, like the outline of a drawing, you can use the key color (black) to make it stand out.
So basically, the CMYK color model helps make sure that all the colors in a printed image look the way they're supposed to by using these four basic colors and mixing them together to make lots of different shades and tones. Pretty cool, huh?