The imperative sentence is used to give an order, a warning, an appeal, an advice, a suggestion, an instruction and in some cases a request to another person, to a group of people or to animals. It is very easy to form the imperative sentence: Simply take the verbs' infinitive form (without the "to" infinitive indicator). Usually the verb will be placed at the beginning of the sentence.
Stand up when I speak to you (order)
Press the button in order to activate the machine (instruction)
Do not touch it, it is hot! (warning)
Take a left at the corner (advice, suggestion)
Close the door.
Give me the keys.
Let's eat something, we are all hungry.
Let us be happy, we are all fine.
In order to create a negative form of an imperative, place "do not", "don't" or "let's not" in front of the infinitive form of the verb (again without "to").
Don't go, I need you here.
Let's not be sad, we are all fine.