Common nouns are what we usually think of when we think of nouns. They name people, places, ideas or things that are not specific. Common nouns are capitalized only if they begin a sentence. They can be singular or plural. The plural is most often made by adding "s" or "es" to the singular, though this is not always the case. Common nouns can also be preceded by definite articles, such as "the," and indefinite articles, such as "a" or "an."
Proper nouns designate specific people, places, ideas or things. They are always capitalized.
There are a huge number of common nouns. For example, people, joy, oceans, country, men and banana are all common nouns.
Barack Obama, Caspian Sea, Minnesota and Delta Airlines are all proper nouns.