A declarative sentence is a statement and always ends with a period. Mars is the fourth planet from the sun. Eating sushi for the first time is an interesting experience.
English majors are quirky.
An exclamatory sentence is an expression of strong feeling and ends with an exclamation point. An imperative sentence gives a command or makes a request and usually ends with a period. However, a very strong command may end with an exclamation point. Please bring me that knife. Take the dog for a walk while you're out.