Okay, so imagine that you have a really cool family with a special last name, like Smith or Johnson. The Stuarts were a family with a special last name too! They were special because they were the rulers of Scotland and eventually became the rulers of England too.
Now, just like you might have a special shirt or hat with your family's last name on it, the Stuarts had something called an "armorial" which is like a picture that represents their family name.
The armorial of the house of Stuart was special because it had different parts to it that each represented something important in their family history. For example, there might be a picture of a lion because the Stuarts were known for being strong and brave like a lion.
The armorial was used as a symbol of the power and prestige of the Stuart family. It was like a way for them to say "we are important and special" without even having to say anything at all!
So basically, the armorial of the house of Stuart was a fancy picture that represented their family name and all the important things about their family history.