GRAMMAR : IMPERATIVE

The imperative 

We can use the imperative to give a direct order :

• Take that chewing gum out of your mouth. 
• Stand up straight. 
• Give me the details. 

We can use the imperative to give instructions.

• Open your book. 
• Take two tablets every evening. 
• Take a left and then a right. 

We can use the imperative to make-an invitation.

• Come in and sit down. Make yourself at home. 
• Please start without me. I'll be there shortly. 
• Have a piece of this cake. It's delicious. 

We can use the imperative on signs and notices.

• Push. 
• Do not use. 
• Insert one dollar. 

We can use the imperative to give friendly informal advice.

• Speak to him. Tell him how you feel. 
• Have a quiet word with her about it. 
• Do not go. Stay at home and rest up. Get some sleep and recover. 

We can make the imperative 'more polite' by adding 'do'.

• Do be quiet. 
• Do come. 
• Do sit down.

Source: (http://www.englishgrammarsecrets.com/imperative/menu.php)