When we talk about the benefactive case, we're talking about how the person or thing that benefits from an action is shown in our language. So, let's say you wanted to talk about how you did something nice for your friend. In English, you would say "I got ice cream for my friend." But in some other languages, you would change the form of the word "friend" to show that they are the one benefiting from your action.
For example, if you were speaking in Finnish, you might say "minä hain jäätelöä ystävälleni." Here, the word "ystävälleni" has an ending that tells us that the friend is the one who benefited from you getting the ice cream.
So, the benefactive case is all about showing who or what is receiving the benefits of an action in a really clear way. It's like a special form of words that we use to make sure everyone knows who we're talking about and what they got out of a situation.