Paul Andersen introduces the Punnett Square as a a powerful tool in genetic analysis. He tries to address major misconceptions that students have when use a Punnett Square. He gives a number of examples of monohybrid crosses and one example of a dihybrid cross. The square is a simple tool that uses the outcome of meiosis to determine possible offspring in a cross.
Source: Bozeman Science
Optional Video: Crash Course - Heredity
I've put this video up before, but at around 7 minutes Hank shows you how to use a punnett square. So it might be worth another look!