Euro NCAP is like a grown-up who checks how safe cars are for you to ride in. He looks at lots of things to make sure you won't get hurt if there's a crash.
Just like how doctors check your heart, eyes, and ears to make sure you're healthy, Euro NCAP checks the cars' brakes, airbags, and lots of other things to give them a score from 1 to 5 stars.
If a car gets a good score, it means it's safer for you to ride in. This is really important because if you're ever in a car accident, having a safe car can protect you and keep you from getting hurt badly.