The imperative tense in English 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. 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.
Close the door.
Give me the keys.
The above form is used if a person gives an order to another person or to a group of people. But if the imperative includes oneself in the group of people who receive the order the words "Let us" or "Let's" are added before the infinitive in the sentence.
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.
The imperative form can also be used to make a request, if you add "please" to the imperative sentence. You can also add "Would you" instead or in addition to "please" (which can be a question or a polite order).
Please come, I need you there.
Please don't go, I need you here.
Stand up when I speak to you (order)
Press the red button in order to run the machine (instruction)
Do not touch it, it is hot! (warning)
Do regular exercise in the morning. (advice, suggestion)