Clause:
A grammatical unit that contains both a subject and a verb. An independent, or main clause expresses a complete thought and can stand alone as a sentence. A dependent, or subordinate clause cannot stand alone as a sentence and must be accompanied by and independent clause.


Example:
"Life moves pretty fast, if you don't stop and look around once in a while, you could miss it."
-Ferris Bueller's Day Off



Explanation: 
In this sentence "Life moves pretty fast" is the independent clause. Ferris Bueller says this to show emphasizes on the importance of life, and how it moves fast. That is really the only purpose of the clause. This is a small clause, one that can seem merely unimportant, but in fact it explains Bueller's view, and can show his personality.