Nouns

Nouns are people (Wayne Gretzky, Prime Minister Pierre Elliot Trudeau, Lawren Harris, the woman), places (Northlands Colosseum, Ottawa, Algonquin Park, the school), or things (a hockey puck, legislation, paint brushes, a desk).

Nouns can be concrete or abstract.  Concrete nouns are available to the senses; we can touch, taste, see, smell, or hear them such as apples, sugar, a book, or the ocean.  Abstract nouns are not available to the senses; they are ideas or concepts such as love, frustration, psychology, or happiness.

There are also proper nouns.  Proper nouns are the name of an person, place, or thing and always begin with a capital letter: Anna, Canada, or Otago University.

Nouns sometimes can be very easy to identify in a sentence by their articles; nouns often follow "a," "an," (indefinite articles) or "the" (definite article).  If you look at the following sentence, you can see that each word that follows a definite or indefinite article is a noun:

The woman walked to the store and bought a fresh carrot and some oranges.

You can see that there are two exceptions here.  First, though "fresh" follows "a," it is not the noun; rather, it describes the noun, "carrot."  Sometimes there may be a describing word (an adjective) between the definite or indefinite article and the noun.

Second, you can also see that there is another noun ("oranges") that is not preceded by a definite or indefinite article.  When nouns are plural (i.e. there is more than one of them--here "some oranges"), they do not follow "a," "an," or "the."  Nouns can follow other words like possessive adjectives (my jacket, your hat, her pants, or its colour) or another noun indicating possession (Michael's friend or the elephant's trunk).

As always, Schoolhouse Rock has a good video:

Resources:

D'Youville College has a good online test for proper nouns.  MyEnglishGrammar has an ok exercise to help you identify nouns.