In basketball, one of the key ways to stop your opponent from scoring is to block their view of the ball. By using your body and hands to shield the ball from them, you make it much harder for them to catch or steal it.
There are a few different ways to do this. One is to simply stand in front of your opponent, making it difficult for them to see around you. Another is to reach out with your arms and hands and block their view that way.
Whatever method you choose, the goal is the same: to make it as tough as possible for your opponent to see the ball. If they can't see it, they can't catch it or steal it. And that means they're less likely to score against you.