Independent and dependent clauses are the building blocks of sentences. An independent clause can stand alone as a complete sentence, while a dependent clause cannot. There are three main types of dependent clauses: noun clauses that function as nouns, adverb clauses that provide details about the verb like time and condition, and adjective clauses that modify nouns and pronouns. Understanding clauses and how they are structured and connected is important for avoiding errors and writing sentences with varied structures.