The Puerto Rican Flag is basically a blue triangle with a white star in the middle of it, with three red lines and two white ones coming out of the triangle.
The three colors are representants of Puerto Rico's three main races: The whites, whose ancestors were the Europeans, the blacks, whose ancestors came from Africa, and the brown skinned, whose ancestors, the Indians, were Puerto Rico's original citizens.
The star is there to symbolize Puerto Rico's political half union with the United States.