Okay kiddo, imagine you have a favorite toy that you really like to play with. You want to tell all your friends about how cool your toy is and why they should get one too. That's just like what companies do with advertising postcards.
An advertising postcard is like a little card that a company makes to tell people about their product or service. It's like a mini poster that's small enough to fit in your mailbox. The company can put pictures and words on the card to show you what the product looks like and tell you what it does.
Sometimes, companies send these cards out to a bunch of people all at once. Other times, they give them out in stores or at events. They might even leave them in piles at places like coffee shops or libraries for people to pick up.
The idea is to get as many people as possible to see the postcard and think "Wow, that looks really cool. I want to learn more!" Then, they might go online or visit a store to buy the product.
So, just like you want to tell your friends about your favorite toy, companies want to tell everyone about their products. And that's why they make advertising postcards!