1. There are two types of adjective clauses: relative pronouns and relative adverbs. Relative pronouns use words like who, whom, whose, which, and that, while relative adverbs use when and where.
2. An adjective clause can be changed into an adjective phrase by removing the subject pronoun and verb "be".
3. Adjective clauses are often used to provide additional information about a noun and are set off by commas, while clauses that serve to identify a noun are not set off by commas.