The document discusses different types of subordinate clauses including nominal clauses, adjectival clauses, and adverbial clauses. It explains that subordinate clauses are dependent clauses that cannot stand alone as sentences. Nominal clauses function as nouns, adjectival clauses function as adjectives, and adverbial clauses function as adverbs. The document also discusses restrictive and non-restrictive adjective clauses, and how punctuation differs between the two types.