An independent clause is a clause that can stand alone as a sentence (it expresses a complete thought). An independent clause, like all clauses, has a subject and verb. For example: The best defense against a atomic bomb is not to be there when it goes off.
A dependent clause (or subordinate clause) is one that cannot stand alone as a complete sentence because it does not express a complete thought. For example: The crew could see the whale, which had surfaced only 50m behind them.
A noun clause is a clause that plays the role of a noun. For example: I've met the man who won the lottery.