The passive voice is a form of sentence construction in which the usual positions of the subject and object of a sentence are reversed. The video below starts with the phrase "The boy throws the ball" (which is in the active voice) and from there provides a clear and simple explanation of how to take this sentence and sentences like it and transform them into the passive voice.
Source: Spinnerrowe via youtube.com
When to and when not to use the passive voice can be tricky to know. Many humanities teachers, for example, do not like sentences written in the passive voice because they believe such sentences lack clarity. In areas such as the sciences, however, the passive voice is considered appropriate and sometimes even required. The PDF below provides a thorough breakdown of the passive voice itself, as well as situations in which it is and is not appropriate.
Source: Creative Commons: The Writing Center, University of North Carolina at Chapel Hill
For writers, the passive voice is like another other form of sentence construction: it is a tool to be used when and as appropriate. In this lesson, you studied both how to create the passive voice and the situations in which its usage is appropriate and inappropriate. Understanding these rules can help you add the passive voice to your writer's toolkit and use it in the most effective ways possible.
Source: Dan Reade