The passive voice is a way of expressing a sentence in which the object becomes the subject.
Examples:
It allows us to shift the focus away from the doer and onto the thing being done.
Example:
The book was written by Jane Austen.
Here, the focus is on the book, not on Jane Austen.
This can be useful when the doer is not important or is unknown.
But don't overuse it, or you might end up like this:
The door was opened by a mysterious figure in a cloak of darkness.
Now, that's just ridiculous.
So, be cautious when using the passive voice.
De-Transitive Voice might be more suitable for that sentence.
But that's a story for another time.
For now, let's just say, the ball was thrown by the player.
And that's all, folks.
And so on, and so forth.