Imagine that you are the boss of McDonald's. Then you have 37,000 restaurants in 120 countries.
It is, of course, very difficult to manage all these restaurants on your own.
So what is a good solution to this problem?
You let some people help you! You lend the restaurants to 120 people who arrange everything in their country! They get to choose, for example, what is on the menu and how it is advertised. In exchange, they only have to give you a part of the money.
That's also how Charlemagne ruled the Frankish empire!