Okay, kiddo, let me explain. A long time ago, in the 1800s, a group of seven islands in the Mediterranean Sea became a part of a bigger country called the United States of the Ionian Islands. These islands were called Corfu, Zakynthos, Kefalonia, Paxi, Ithaca, Lefkada and Kythira.
Think of it like this - Imagine you have a big box with many smaller boxes inside it. The seven Ionian Islands were like those smaller boxes. They were a part of Greece, which was the bigger box. But then, for a short time, those seven islands became a separate country called the United States of the Ionian Islands.
It was similar to when you and your friends make a secret club and have your own set of rules for a while before you go back to being friends in your usual group. During that time, the United States of the Ionian Islands had its own flag, leaders, and rules, but eventually, the islands became a part of Greece once again.
So, to sum it up, the United States of the Ionian Islands was a small country made up of seven islands that tried to be independent from Greece for some time but eventually became a part of Greece again.