When we talk about beginner defense for beach volleyball, we're talking about two players, one the blocker, and two the defender. There's also another kind of defense where both people are defenders, and no one's blocking at the net. But typically, you have a blocker and a defender.
The blocker presses their hands over the net, tries to re-direct the ball, or to block the ball with their hands. The defender reads around the blocker, and tries to dig the ball.
When we talk about digging, usually you're trying to dig with your arms together, like this. Sometimes you can't get to the ball in time and you have to use one arm, and you try to create a nice, flat surface for the ball to lift off of your arm. Other times, the ball comes too high at your face, and you have to dig with your hands. This is where the rules of beach volleyball come into play.
You can't open hand dig with your fingers, unless it's considered a hard driven ball. If not, you have to put your hands together like this. And these are the basics of defense in beach volleyball.