Alright little buddy, so a long time ago in Japan, there was a city called Nara. Some guys who were in charge of another city nearby didn't like Nara and wanted to take it over. So they got their soldiers together and went to attack Nara.
Now, Nara was a big and strong city. It had walls all around it to protect itself. People inside the city were afraid of the attackers, but they didn't just hide. They got ready to fight!
The attackers began to surround the city. Imagine a big circle of soldiers all around Nara. They were trying to get in and take over the city. But the people inside Nara were smart. They had lots of weapons and ammunition to fight back.
So the attackers kept trying and trying for days and days. They would shoot at the walls and try to break them down. But the people inside Nara didn't give up. They also had clever tricks up their sleeves, like using fire and smoke to make it hard for the attackers to see.
Finally, after many days of fighting, the attackers realized they couldn't win. They gave up and went back to their city. The people of Nara had won! They were happy and relieved that their city was safe from the invaders.
And that, little buddy, is what the siege of Nara was all about. It was a big fight over a city, and the people inside the city worked hard to protect it and win.