One problem that many writers have when they write is the use of passive rather than active voice. This is a problem, because the frequent use of passive voice can ruin writing. Unfortunately, most people don't understand or don't care about the use of passive and active voice, so they don't take care to pay attention to this important detail in their writing.
Who needs this information? You, if you are writing something. When you communicate through writing, you need to be able to communicate well. If you understand a little more about your language, you can use your language more effectively. If you don't understand how to play the guitar, how are you supposed to play a song? If you don't understand how to swing a hammer, how are you supposed to drive a nail without bending it? If you don't understand how to use a gas pedal, how are you supposed to drive a car anywhere? You may find these details boring, but they are necessary when communicating through the written word.
I can attempt to walk through passive and active voices and give a bunch of information that you are never going to understand, but it would be better to take a look at a pair of examples:
The movie sucks donkey balls.
Donkey balls are sucked by the movie.
Do you notice the essential difference between the two sentences above? Allow me to explain why it is so.
In both sentences, the movie is the acting agent. What is the movie doing? It is sucking. What is it sucking? Donkey balls.
In active voice, the subject of the sentence (i.e. the movie) acts upon the object (i.e. donkey balls).
In passive voice, the subject of the sentence (i.e. donkey balls) is being acted upon by the object (i.e. the movie). Or, put another way, the object is acting upon the subject.
Do you remember your subjects and objects? Yeah, I didn't either for a long time. Essentially, the subject is the main topic of the sentence and the object is modifying the sentence. In point of fact, the object is not necessary. For example, look at these sentences:
The movie sucks.
Donkey balls are sucked.
Both are grammatically correct and valid. Both refer to the main action of the previous sentences. But only by combining the movie, the sucking, and the donkey balls into the same sentence does the actual action become clear: that the movie is the thing that is doing the sucking of the donkey balls.
Though the action can be the same in active or passive voice, the use of one or another changes the emphasis of the sentence. In just about any sentence, the subject is the most important noun in the sentence (and if you don't know what a noun is, then you are in way over your head) and the object is the noun of less importance. In both active and passive voices, the movie is the one doing the acting. In both active and passive voices, the donkey balls are receiving the action of the movie. But only in active voice is the principal actor (the movie) in the position of most importance (the subject).
So let's examine the sentences again:
The movie sucks donkey balls.
In this case, the movie is the important thing. It doesn't necessarily matter if the movie sucks donkey balls, specifically. It could be horse balls or kangaroo balls. It could be chicken shit. It could be homeless men's assholes. It could be witches' tits. The principal part of the sentence is the movie and it is vital that we express that it sucks.
Contrast that with:
Donkey balls are sucked by the movie.
In this case, the donkey balls are the important part of the sentence. It isn't as vital that it was the movie, the play, the album, or the Cleveland Cavaliers. In the passive voice, what is important is that donkey balls, specifically, are being sucked by something.
There are some instances where the passive voice is necessary and preferable. But I can't think of any examples offhand, so you'll just have to come up with some of your own. So, unless you have a compelling reason for passive voice, use active voice when you are writing.
And why should you use active voice? Why will your readers prefer active voice? Why will your English teachers take points off of your paper for passive voice? Because the active voice's sentence structure reinforces the action of the sentence! In active voice, the principal actor in the sentence—the movie—is in the principal location of the sentence—the subject.
Contrast that with passive voice, in which the principal actor is in a reduced role—the object. This diminishes the vigorousness of the actor. In passive voice, the principal actor in reality is the movie, but the principal actor in the sentence structure is the donkey balls. Therefore, a passive-voiced sentence is actually working against its own meaning.
Thus we come to the very reason that the verb voices are called "active" and "passive". In the active voice, the subject of the sentence is actively doing something and the entire sentence is much more active as a result. In the passive voice, the subject of the sentence is passively receiving the action of the sentence.
And in the rather staid world of the written word, wouldn't you prefer to have sentences that have some vitality to them? Reading is boring enough on its own; don't make it any more boring with the passive voice.