The four types of sentences in the English language are declarative, interrogative, exclamatory and imperative. A sentence is classified as one of these types according to its function, and punctuation varies between the different types.
A declarative sentence makes a statement, and its ending punctuation is a period. In this type of sentence, the subject usually comes before the verb.
An interrogative sentence asks a question and ends with a question mark. Often part of the verb precedes the subject of the sentence.
An exclamatory sentence ends with an exclamation point and shows strong emotion. A declarative sentence can become an exclamatory sentence if it is said with strong feeling, in which case the exclamation point replaces the period at the end.
An imperative sentence gives an order or request. It can end with a period or exclamation point depending on the amount of emotion intended. These sentences often begin with a verb and have an understood "you" as the subject.