Kaiserliche Reichspost is a big word that means "Imperial Postal Service". Just like how we have mailmen and mailboxes to send letters and packages, the Kaiserliche Reichspost was the way people sent mail back when there was an empire called Germany.
The postal service worked by having big buildings called post offices where people could go to send letters and packages. They would give their letter or package to the people working there, and then the postal workers would make sure it got to the right place. They did this by putting special stamps on the letters and packages with the address and where it needed to go.
The Kaiserliche Reichspost was very important because it helped people stay connected even if they were far away. Imagine you wanted to send a letter to your friend who lives in another city, but you didn't have the Kaiserliche Reichspost. You would have to travel all the way to their city just to give them a letter, and that would take a very long time.
But because of the Kaiserliche Reichspost, people could send letters and packages to each other from far away without having to travel. It made communication easier and faster. Today, we still have postal services that help us send letters and packages just like the Kaiserliche Reichspost did a long time ago.