Sentence types are categorized based on their structure and purpose. The four main types are declarative, interrogative, imperative, and exclamatory. Declarative sentences make statements, interrogative sentences ask questions, imperative sentences give commands, and exclamatory sentences express strong emotions. Each type serves a different function in communication. For example, a declarative sentence like "The sky is blue" provides information, while an interrogative sentence such as "Is the sky blue?" seeks clarification. Understanding these sentence types helps improve writing and enhances effective communication in both spoken and written forms.