Okay, kiddo, let me explain the Pact of Umar to you.
Once upon a time, a long, long time ago, some people called Muslims ruled over some other people called Christians and Jews. The Muslims were in charge of the land (like the king or queen of a castle) and the Christians and Jews lived in the land with them.
However, the Muslims wanted to make sure that everyone followed their rules and beliefs. So they made a promise, called the Pact of Umar, with the Christians and Jews.
This promise said that the Christians and Jews could keep following their own religion, but they had to pay a special tax to the Muslim leaders. They also had to follow some rules, like not building new churches or temples, not making too much noise when they pray, and not showing off their religion in public.
In return, the Muslims promised to protect the Christians and Jews and let them live in the land peacefully.
So basically, the Pact of Umar was like a big agreement between the Muslim rulers and the Christians and Jews who lived in their land. It said that everyone had to follow some rules, but they would be safe and respected as long as they did.