Imagine a big castle with a king and queen who rule over everything inside the castle walls. But sometimes the king and queen need help to take care of the castle and make sure everything runs smoothly.
So they pick someone they really trust, like a prince or princess, to help them. This person is called a duke or duchess. They have their own special area within the castle where they help take care of things like welcoming visitors, making sure everyone has enough food, and making sure everything is clean and tidy.
Now, back in the olden days, there was a big area called Austria. The king and queen needed help taking care of this area, so they picked someone they really trusted, like a prince or princess, to be the duke or duchess of Austria. This person helped take care of everything in Austria and made sure the people who lived there were happy and felt safe.
Eventually, the duke or duchess of Austria became so important that they even got to be in charge of Austria all by themselves. They were kind of like a mini-king or queen, but they still had to listen to the big king and queen who lived in the big castle. And that's how the Duchy of Austria became a very important place in history!