Economies of agglomeration is like when you have lots and lots of stores or factories or houses all in one place. When things are all in one place, something magic happens, and it gets cheaper and easier to make and sell things.
Imagine you're a toy maker. When you make toys, you need lots of things like materials, workers, and machines. But if you make toys all by yourself, it would be hard and expensive to get everything you need. But if you work in a place where there are a bunch of toy factories, you can share things with other toy makers. Maybe you can borrow raw materials from someone else or buy things in bulk together, and that makes it easier and cheaper to make your toys.
This is also good for people who want to buy toys. If there are lots of toy stores all in one place, it's easier for people to find the toys they want, and they can compare prices to save money. It's like going to a big toy store where you can find everything you need instead of having to go to many different places.
The same thing happens with things like houses and shops. When you have lots of houses or shops all in one place, it's easier for people to find what they need, and things can be sold more cheaply. People like living in places where there are plenty of shops, restaurants, and entertainment options, so they move there. Because so many people are in one place, it attracts more businesses, and the area becomes popular.
Economies of agglomeration can be great for everyone involved, but it can also have problems. For example, if too many people or businesses are in one place, it can become too crowded or the environment can become polluted. However, if everything is done correctly, economies of agglomeration can make people's lives easier and more enjoyable.