Imagine you want to have a yummy chocolate chip cookie. You don't have all the things you need to make it, so you need to go to the store. The store needs to go to a bigger store called a warehouse to get all the things you need to make the cookie like flour, sugar, chocolate chips, and butter. The warehouse needs to get these things from even bigger places like farms and factories that make these things. All of these steps together make up the "supply chain" of the cookie.
Now imagine bigger things like toys or clothes. There are lots of steps and people involved in making them and getting them to the store for you to buy. This is why supply chains are very important because they help get you the things you want to buy from all over the world!