Simple Present tense

An Active sentence in the simple present tense has the following structure:
Subject + first form of the verb + object

A passive sentence in the simple present tense has the following structure:
Object of the active sentence + is/am/are + past participle form of the verb + by + subject of the active sentence

Changing an assertive sentence into the passive

Active: I write a letter.
Passive: A letter is written by me.
Active: I help you.
Passive: You are helped by me.
Active: I love my parents.
Passive: My parents are loved by me.
Active: We love our country.
Passive: Our country is loved by us.

Changing a negative sentence into the passive

Active: I do not write a letter.
Passive: A letter is not written by me.
Active: I do not abuse my servants.
Passive: My servants are not abused by me.
Active: I do not write novels.
Passive: Novels are not written by me.
Active: He does not tease her.
Passive: She is not teased by him.

Changing an interrogative sentence into the passive

Structure: Is/are/am + object of the active verb + past participle form of the verb + by + subject of the passive verb

Active: Do you write a letter?
Passive: Is a letter written by you?
Active: Do you write stories?
Passive: Are stories written by you?
Active: Does she make candles?
Passive: Are candles made by her?
Active: Who does not obey you?
Passive: By whom are you not obeyed?
Active: Which newspaper do you read?
Passive: Which newspaper is read by you?
Active: Does she do her duty?
Passive: Is her duty done by her?

Notes:

The object of the active verb becomes the subject of the passive verb. Therefore, sentences which do not have an object cannot be changed into the passive. The following sentences, for instance, cannot be changed into the passive because they do not have objects.

The old man sat in a corner.
The child sleeps.
The wind blows.
The dog barks.
The fire burns.
He laughed aloud.