Okay kiddo, so an ulpana is a place where people go to learn how to speak Hebrew really well. It's kind of like going to a special school where the teachers only speak Hebrew, so you have to listen very carefully and practice speaking too!
Ulpana is mostly for kids who live in Israel and need to learn Hebrew because it's the main language there. But sometimes grown-ups go to ulpana too, like if they move to Israel and they don't know much Hebrew yet. It's a lot of hard work, but it's important to know the language so you can communicate with everyone around you.