Classical unities are rules that people who create plays follow to make a good story. Think of them like a recipe for a cake. Just as you need certain ingredients in the right amounts for a delicious cake, a playwright needs to follow certain rules for a good story.
The first rule is unity of action. This means that the play should have one main storyline. It's like making a cake with one flavor, instead of mixing a bunch of different flavors together.
The second rule is unity of time. This means that the story should take place in a short amount of time. Just like how it's easier to make a cake that bakes for only 30 minutes instead of one that takes hours.
The third rule is unity of place. This means that the story should happen in one location - like a room or a city. Just like baking a cake in one oven instead of trying to use different ovens at different temperatures.
By following these rules, a playwright can create a story that is clear, easy to follow, and enjoyable for the audience.