There are four main types of sentences: declarative, interrogative, imperative, and exclamatory. A declarative sentence states a fact or opinion, such as "The sky is blue." An interrogative sentence asks a question, like "What time is it?" Imperative sentences give commands or requests, for example, "Please close the door." Lastly, exclamatory sentences express strong emotions, such as "What a beautiful day!" Each type serves a different purpose in communication.