A sentence is a group of words that makes sense on its own.
A full sentence expresses a complete idea.
A sentence consists of at least a subject and a predicate.

Verb        Object        Complement

The verb plus the object or complement form the ‘predicate’. Not all sentences contain an object or complement as part of the predicate.
In every sentence the most important word can be said to be the verb. A verb shows action or activity or work done by the subject.
Sentences can be statements, questions, exclamations or commands.