What does a Punnett square show us?
The possible outcomes of different gene traits.
If you were to take a bean with the traits of being yellow and being green, and a bean with the traits of green and green again, with yellow being the dominant trait, you could use a Punnett square to assess how many offspring might be green or yellow.
As you can see, two beans will be yellow and two beans will be green according to the square.
Hope this helps!