What is independent and dependent clause?

An independent clause is a part or is a sentence,that has a verb and subject,and can be a sentence all by its self.A dependent clause is part of a sentence that has a subject and ver,but CAN NOT be a sentence alone! ex.independent clause-John is in it.(Can not be a sentence ,John is in what?) ex.dependent clause-John is in the red box.(Can be a sentence,the sentence tells what John is in.)