English/Parts of Speech/Verbs/Moods/Imperative Mood

A) an order, a suggestion, a request, a warning to an individuum or group of which the speaker/writer is

  not a member!:

  Learn these words! Fight for your rights! 

  it has the form of the infinitive of the verb (without to)

  negation with "don't"/"do not"

  Don't underestimate the power of intuition. Do not drink and drive.

  it can be made more emphatic, if we put "do" in front of the imperative form:

  Do wash your hands now. Do stop making a nuisance of yourself.

The imperative mood

has sometimes an exclamation mark (!)

has two forms:

B) an order, a suggestion, a request, a warning, a summons to a group of which the speaker/writer is

  a member:

  Let's find an answer. Let us concentrate on these statistics.

  negation: "Let's not", "Don't let's"

  Let's not forget this important fact. Don't let's be too inquisitive now.

  it can be made more emphatic, if we put "do" in front of the imperative form:

  Do let's keep our nerves.

  the question tag for sentences with "Let's" is "shall we"?

  "Let's phone granny, shall we?"