Se trata de una explicación de la forma pasiva

2.  The passive is a form of be+ a past
participle.
Ej: is written, as built.
• Use: we use the passive voice when the
important thing is the action in a sentence.
The sentences must have a direct objets

3. Active Passive
Present Simple They write a letter The letter is written
Present Continuous They are writing a letter The letter in being written
Present Perfect They have written a letter The letter has been written
Past Simple They wrote a letter The letter was written
Past Continuous They were writing a letter The letter was being written
Past Perfect They had written a letter The letter had been written
Future (Will) They will write a letter The letter will be written
Future (going to) They are going to write a letter The letter is going to be written
Modal verb ( Should) They should write a letter The letter should be written
Modal verb (Can) They can write a letter The letter can be written
Modal verb (Must) They must write a letter The letter must be written

4. •What is the difference?
- Active: Mary wrote a letter
In this sentence we are talking about Mary. So, she is doing the
action.
- Passive: A letter was written by Mary
Here we are talking about the letter and the new information is
Mary
• Special Structures
In the following sentences we can have two structures because
we have two subjects which are not doing the action:
Active Passive
Tom gave a present to Mary A present was given to Mary
Tom gave Mary a present Mary was given a present

5. 1) She tidied the bedroom
- The bedroom was tidied
2) They celebrated a party
- A party was celebrated
3) We will prepare a dinner
- A dinner will be prepared
4) He is reading a book
- A book is being read
5) I must do the shopping
- The shopping must be done