Sentences and style

When using the active voice, the subject of the sentence does the verb to the object. 

E.g., The dog chased the cat (subject=dog, verb=chased, object=cat).

When using the passive voice, the subject of the sentence is acted upon.

E.g., The cat is being chased by the dog. (subject=cat, verb=is being chased, object=dog).

Using the active voice makes your writing clearer and more to the point.  It helps to avoid wordiness because the active voice is more direct and requires fewer words to communicate the message.