Nusach is like a special way that Jewish people say prayers. It's like a recipe for prayer that has been passed down from older people to younger people over a long, long time. Just like how when your mommy makes her famous pancakes, she has a recipe with special ingredients and instructions, the Jewish people have special instructions for how to say their prayers.
It's like a special language that only Jewish people know how to use to talk to God. Some Jewish people say their prayers one way, while others say it a different way, but they all have the same goal of talking to God in the way that feels most meaningful to them.
When you go to a Jewish service, you might notice that some people are saying words differently than others or that some words are repeated more times than others. That's because of nusach! And just like how different people like different types of pancakes, different Jewish people like to use different nusachs depending on where they come from or what feels most special to them.