A sentence is a group of words that makes a complete thought. It always begins with a capital letter and usually ends with a period.
A fragment is a separated part of a sentence that does not make a complete thought.
A declarative sentence makes a statement. It ends with a period.
An interrogative sentence asks a question. It ends with a question mark.
An imperative sentence gives a command or makes a request. It ends with a period, or an exclamation point.
An exclamatory sentence shows sudden or strong feeling. It ends with an exclamation point.
A run-together sentence is a poorly written sentence containing too many ideas joined by and, and so, or and then.