Punnett Squares are a way to find the trait for an offspring. They are used in squares of four to give a percentage to give a probability answer. For example, black is the dominant trait and blond is the recessive trait. If there are a heterozygous mother and a homozygous recessive father to find out whether the offspring is going to be blond haired or black haired is by putting the heterozygous on the top of the Punnett square and finish the Punnett square by having the top letter which is one of the allies of the parents and putting it together with the other Allie letter to make a new trait. When you are finished you can determine if the offspring is going to be blond or if the offspring is going to be blond or dark haired. In this example the offspring is going to have a 50% of being blond and a 50% percent of being black haired.
Punnett are very useful when you are trying to find a future trait of an offspring. I know this can be very useful when you are trying to find out the trait of an offspring. I know this might be helpful for you some day, but one thing that I don't understand is how you know wen you are heterozygous or not. Can you explain?