Define communicative types of sentences

Sentence Structure: The Fab Four
In Clauses, you learned that there are two types of clauses: independent and dependent. Recall that independent clauses are complete sentences because they have a subject and verb and express a complete thought. Dependent clauses, in contrast, cannot stand alone because they do not express a complete thought—even though they have a subject and a verb. Independent and dependent clauses can be used in a number of ways to form the four basic types of sentences: simple, compound, complex, and compound-complex. Time to make their acquaintance.

These types of sentences are more intended for the speaker's sake than for any potential listener. They are meant more for the speaker's immediate wants and needs. These sentences tend to be less intentional (out of frustration for example), in general more literal, more primitive, and are usually about the here and now. Because of these features, it is generally speculated that this is pretty much the basis or limitation of any form of animal communication. (Speculated because scientists will never truly be able to understand non-human forms of communication like we do our own; although studies with "talking" primates have clued us in to a certain degree.)
Communicative sentences

Exclamatory
An exclamative or exclamatory sentence is released because of, and expresses strong emotion. They many times feel like involuntary reactions to a situation, yet they can technically be stifled if need be. And while exclamatives most usually manifest themselves as one or two word interjections, they can also come as major sentences. They are essentially unfiltered vocalizations of our feelings, and a form of self-talk because they are directed either at the speaker themself or at nobody in particular. In punctuation, an exclamative is ended with an exclamation mark.
Ouch!
I'll never finish this paper in time!

Imperative
An imperative sentence gives anything from a command or order, to a request, direction, or instruction. Imperative sentences are more intentional than exclamatory sentences and do require an audience; as their aim is to get the person(s) being addressed either to do or to not do something. And although this function usually deals with the immediate temporal vicinity, its scope can be extended, i.e. you can order somebody to move out as soon as you find yourself a job. The negative imperative can also be called the prohibitive and the inclusive plural imperative, the hortative. It is debatable whether the imperative is only truly possible in the second person. The vocative case of nouns can be said to indicate the imperative as well since it does not seek information, but rather a reaction from the one being addressed. An imperative can end in either a period or an exclamation point depending on delivery.
Look at me!
After separating them from the yolks, beat the whites until they are light and fluffy.

Informative sentences
Informative sentences are more for the mutual benefit of both the listener and the speaker, and, in fact, require more of an interaction between both parties involved. They are more intentional or premeditated, less essential, more cooperative, and they aim to either provide or retrieve information, making them quintessential abstractions. But perhaps the most differentiating quality that distinguishes informative sentences from the communicative is that the former more naturally and freely make use of displacement. Displacement refers to information lost in time and space which allows us to communicate ideas relating to the past or future (not just the now), and that have taken or can take place at a separate location (from here). To an extent, this is one of the biggest differences between human communication and that of other animals.

Declarative
The declarative sentence is the most common kind of sentence in language, in most situations, and in a way can be considered the default function of a sentence. What this means essentially is that when a language modifies a sentence in order to form a question or give a command, the base form will always be the declarative. In its most basic sense, a declarative states an idea (either objectively or subjectively on the part of the speaker; and may be either true or false) for the sheer purpose of transferring intel. In writing, a statement will end with a period.
Roses are red and violets are blue.
She must be out of her mind.