Imparative Sentence

The word "imperative" is derived from the term "emperor". Emperors gave commands, and imperative sentences are commands. Imperative sentences consist of predicates that only contain verbs in infinitive form; verb phrases are not allowed. Imperative sentences are generally terminated with an exclamation mark instead of a period. Definition of an imperative sentence An imperative sentence: is used to give a direct command to someone can end with a period or an exclamation mark depending on the degree of the command containing the word "please" should end with a period is commonly used in speech but not often in writing

Examples of imperative sentences Be quiet! Please hand in your homework.

what is imperative sentence and when to use

• Imperatives do not show personal contrasts. It always implies
a second person subject. It does not show tense change. It refers always
to future.

In the above passage, sentences in bold letters/italics do not have
the subject, the addressee, ‘you’ which is traditionally omitted.
Realise things could be worse.

Don’t think too much on bad things.

Note: Let your experience fully satisfy you. (Refer to ‘Theme Focus)
Let’s not waste time. (Another form of using the word ‘let’.)

• Principal uses of imperatives:
1. Direction/instruction, advice:Keep this syrup in a cool dry place.
Don’t go near the fire.
Go straight along this road.
Take a left turn at the signal.

2. Commands or requests for performance:
Answer the following questions.
Find/the volume of a sphere of radius 2 cm.

3. Preliminaries to an argument/demo:
Let’s take a round-bottomed flask.
Suppose we grant him leave for a month.

4. Subject with imperatives:
‘Someone answer the question’.
Note: ‘Someone can answer the question,’ is not imperative but
declarative.  

                     You can use the imperative form to give an order, to give a warning or advice, and (if you use "please") to make a request.
To make the imperative, use the infinitive of the verb without 'to':

"Come here!"
"Sit down!"

To make a negative imperative, put "do not" or "don't" before the verb:

"Don't go!"
"Do not walk on the grass."

The imperative can be used for all subjects (you, he, they and we), but you can also use "let's" before the verb if you are including yourself in the imperative:

"Let's stop now."
"Let's have some lunch."

The negative of "let's" is "let's not":

"Let's not argue!
"Let's not tell her about it."

Warnings

You can use the imperative to warn someone of danger. All the words in the warning are stressed, but the last word has a higher tone than the first word:

"Watch out!"
"Look out!"
"Don't cross!"

Advice

When you give advice using the imperative, the words are stressed normally:

"Eat an apple – it's much better for you than a biscuit!"

"Don't tell him you're resigning now! Wait until Monday when he's in a better mood."

You can often read articles in magazines that give advice on a subject. Sometimes, this advice is presented as "Dos and don'ts".

Requests

You can also use the imperative to make a request, but you should use a polite word before the verb:

"Please take a seat."
"Please wait here."
"Please hold the line."
"Please don't smoke here."

Exercise of  imperative sentences
Exercise 1
Exercise 2
Exercise 3

Resource

http://www.learnenglish.be/gr1_impe_ex2.htm
http://examples.yourdictionary.com/imperative
http://funeasyenglish.com/american-english-grammar-imperative-sentence.htm