http://www.englishpage.com/vebpage/verbtenseintro.html
Defines a “verb tense”, gives a tutorial between active and passive verbs and exercises .In the active verb form, the thing doing the action is the subject of the sentence an the thing receiving the action is the object i.e.
The professor teaches the students
(Subject) (Active verb) (Object)
(Doing action) (recieving action)