Active and Passive Voice: 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 passive:
Active: I write a letter.
Passive: A letter is written by me.
Active: I help you.
Passive: You are helped by me.
 
Changing an negative sentences into 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.

Changing an interrogative sentence into 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?