The pronoun substitutes for a specific noun, called its antecedent. When Bing came home, he ate two sandwiches. When Bing came home, Bing ate two sandwiches. Think before you act. Henry is studying English.
Adjectives modify, or describe a noun or pronoun.
Most adjectives come before the noun in a sentence. A list of adjectives is usually separated by commas. Isabel has a big house . This book is fantastic. The dull, boring, uninteresting lecture went on for over one hour.