A declarative sentence is a statement that provides information or expresses an idea. It typically ends with a period and can be either true or false. For example, "The sky is blue" is a declarative sentence because it conveys a fact about the sky. These sentences are the most common type of sentence used in everyday communication. They can be simple, like "I like apples," or more complex, such as "The cat sat on the mat while the dog barked." Declarative sentences help convey thoughts clearly and effectively.