The passive is very easy to form:
- subject + verb to be (in relevant tense) + past participle
Just change the verb to be to whatever tense you need. The past participle never changes.
There are passive infinitives and gerunds which are also formed with the verb to be:
- The work should be finished by Friday.
- No work needs to be done over the weekend.
- Being punished for bad behaviour is normal at school.
- Potatoes have to be washed before being cooked.
The agent would be the subject of an active sentence. It is introduced using by:
- That film was directed by Hitchcock. (Hitchcock directed that film)
- The dinner is being cooked by my sister. (My sister is cooking the dinner)
- The prisoner was shot by the police trying to escape. (The police shot the prisoner trying to escape)
You don't need to include the agent if you don't know it, if it doesn't matter, or if it's obvious:
- He was arrested yesterday (by the police, obviously)
- The building I live in was built in the 1920s (but I don't know who built it, and it doesn't matter anyway)
- You aren't allowed to smoke in here (by law? by the management?)
This is the part Spanish people don't like at all. However, this form is often used in English, especially in things like newspaper reports, or news bulletins.
- It + passive reporting verb + that + clause
- Subject + passive reporting verb + to infinitive*
*Remember that different types of infinitive can be used (simple, continuous, perfect or perfect continuous: to work, to be working, to have worked, to have been working).
Both these structures are used, but the first one is probably the most usual because it can be used with almost any sentence:
- It is thought that the politician is accepting bribes.
- The politician is thought to be accepting bribes.
- It is said that twenty people died in the explosion.
- Twenty people are said to have died in the explosion.
- It is believed that the Prime Minister is on the point of resigning.
- The prime minister is believed to be on the point of resigning
- It was known that the politician had been taking drugs for ages.
- The politician was known to have been taking drugs for ages.
The equivalent structure in Spanish is often the reflexive:
- Se dice que, se supone que, se cree que...
Some of the verbs you can use with this structure are believe, consider, discover, hope, know, report, say, think, understand, etc.