How does a color printer print out color using only three colors? What is the dot formation of these colors?

I need to know how printers print out colored pictures using only three colors. How do these colors form pictures and what is the dot formation of them?How does a color printer print out color using only three colors? What is the dot formation of these colors?
The three colors used are red, blue, and yellow. Out of these colors, you can make any other color. Computers measure precisely how much red, blue, and yellow are used to make the new color.