In active voice, the subject (person, place, thing, idea) comes before the verb (action).
Juan wrote the essay.
Aims Community College provides students with writing tutors.
From a news headline: “Florida man abducts former girlfriend in Wisconsin.”
The verb comes before the subject, seemingly as if the verb is performed upon the subject. Or sometimes, the subject is completely lost.
The essay was written by Juan.
Students are provided with writing tutors by Aims Community College.
From the same news headline: “Wisconsin woman abducted.”
The active voice is clear, to the point, and lets us know who is completing the action. In fact, in the last example, the passive voice leaves out the man who actually did the abducting. This type of language can be confusing at best. There are exceptions, such as when the noun performing the action is obvious, unimportant, or unknown. For instance, the passive voice is often used in scientific reporting, where the emphasis is placed on the action.
“A successful operation was performed” may be preferable to “The doctor performed a successful operation” because it highlights the operation itself, rather than the doctor.
“Largest black hole ever discovered” may be more to the point than “Dr. Physicist Astronomer discovers largest black hole ever recorded.”
The above headline may be using passive voice to highlight the action of the rescue instead of the wilderness experts who rescued the hikers.
However, when in doubt, go active.