Imagine you are on a playground and there is a big ball in the middle. If you roll a smaller ball near the big ball, it will start to go towards the big ball. This is because the big ball has a gravitational field, which means that it pulls things towards it.
Now imagine that instead of the playground, you are in space. The big ball could be a planet or a star, and the smaller ball could be a spaceship or a satellite. The planet or star has a big gravitational field because it has a lot of mass, or stuff that makes it heavy.
The gravitational field is like a force that pulls objects towards it. The strength of the gravitational field depends on how much mass the object has. The bigger the mass, the stronger the gravitational field.
So, if you are close to a large object like a planet, its gravitational field will be very strong and you will feel like you are being pulled towards it. This is why astronauts have to wear special suits with rocket packs when they go into space – otherwise they would get pulled towards the planet and crash into it!
To sum it up, a gravitational field is a force that pulls objects towards a big, heavy object like a planet or a star. The strength of the gravitational field depends on how much mass the object has.