Contrary to popular belief, the passive is a 'voice' not a tense, but it can be used in different tenses - the present, past or future for example.
Confusing huh? So when should you use the passive voice?
It is used much less than the passive voice in English, nonetheless it is used. The passive is used when the subject doing the verb is irrelevant, and the focus is placed on the object of the verb - for example:
Active: Ich singe das Lied
I am singing the song
Passive: Das Lied wird von mir gesungen
The song is being sung by me
So how do you form the passive voice?
1. To form the passive, German uses werden (to become) + the past participle, while English uses "to be."
2. The word "song" (das Lied) in the ACTIVE sentence is an object being acted upon ( In the PASSIVE sentence the former object (Lied) becomes the subject, while the former subject (I, ich) is now the agent (by me/von mir).
3. Only transitive verbs (those that take a direct object) can be made passive. The direct object (accusative case) in the active voice becomes the subject (nominative case) in the passive voice.
A passive voice sentence may or may not include the "agent" (by whom something was done). If the agent (by me, by John) is a person, it is expressed in German with avon-phrase: von John (by John). If the agent is not a person, then a durch-phrase is used:durch den Wind (by the wind)
Here are some examples of the passive voice being used in different tenses:
Perfect: Das Lied wurde gesungen
The song was sung
(Subject + imperfect of werden + past participle)
Pluperfect: Das Lied ist gesungen worden
The song has been sung
(Subject + perfect tense of werden + past participle)
Present: Das Lied wird gesungen
The song is being sung
(Subject + present tense werden + past participle)
Future: Das Lied wird gesungen werden
The song will be sung
(Subject + future tense of werden + past participle)