Okay kiddo, so the Oppian Hill is a place located in Rome, Italy. It's like a big hill made of dirt and rocks, kind of like a big pile of sand at the beach.
A long, long time ago, back when Rome was just a small city, the people who lived there first used the Oppian Hill to build their homes on. They used the rocks and dirt to make walls and roofs for their little houses.
Then, as the city grew bigger and bigger, the Oppian Hill became an important place for the Romans. They built big, fancy buildings on top of the hill like temples and palaces. These buildings were used for important things like government meetings, ceremonies, and even parties.
But over time, the Oppian Hill changed a lot. The big, fancy buildings were destroyed and new buildings were built in their place. Now, the Oppian Hill is mostly just a nice place to go for a walk or a picnic. People can also visit some of the ancient ruins that are still there, like the ruins of the Baths of Trajan, which were Roman public baths from a long time ago.
So that's the Oppian Hill in a nutshell, kiddo. It started out as a place for people to build their homes on, but became an important place for the Romans to do important things. Now it's just a nice place to visit and explore some old ruins.