Screen printing is a method of printing in which a mesh screen is used to apply ink onto a textile. A separate screen is used to print each color or area, for example:

(if your designs has 3 colors, it will take 3 screens to print your design. If your design is going to be printed in 2 different areas, it will take a screen for each area and color.)

A 2 color design on the front and a 2 color design on the back of a shirt will take 4 screens.
Even if the colors on 1 side are the same as the colors on the other side, they are in different areas therefore, it will take 2 screens for each side.

Screen printing is the oldest, most popular, most durable and most economical way to print.

90% of all the item you see printed are screen printed.