There are actually more than two classifications of nouns, but two of the most common and important ones are:

1. Common Nouns: These refer to general categories of people, places, things, or ideas. They are not capitalized unless they start a sentence.

* Examples: dog, city, book, happiness

2. Proper Nouns: These refer to specific people, places, things, or organizations. They are always capitalized.

* Examples: Fido, New York City, The Bible, Amazon

Let me know if you want to explore other classifications of nouns, like concrete vs. abstract, countable vs. uncountable, or collective nouns.