How do you use a punnet square?

Depending on how many genes you are comparing, punnet squares will be of different sizes. Let's just say you are dealing with a monohybrid crossing. The allels you are comparing is B:brown eyes and b:blue eyes. For example, the female's genotype is Bb (which means she has brown eyes) and let's say your male's genotype is Bb as well. Draw a 3x3 square: the two squares in the first column will each have one allel and same goes for the first row. I'll insert an example.