To send a message to someone, you have many choices. You can call the person on a cell phone. You can send them a text message or an instant message. You can send them an email. Can you imagine a world where none of that existed?
The Internet wasn't used widely until the 1990s, so there wasn't much email and instant messaging before then. Cell phones weren't popular until the early 1990s, so phone calls had to be made from home phones. Earlier still, there was no television, no radio, and no telephone. Communication was much harder in those days. What would you do to send a message to a friend?
You'd probably write a letter on a piece of paper and mail it. A truck would take your letter to the post office in your friend's town, and then it would be delivered to your friend's mailbox.