But there is a lot more to nouns than just concrete people, animals, places, or things. It is also abstract ideas. Here's a larger explanation of nouns from the University of Ottawa.
You always write a proper noun with a capital letter, since the noun represents the name of a specific person, place, or thing. The names of days of the week, months, historical documents, institutions, organizations, religions, their holy texts and their adherents are proper nouns.
Last year, Jaime had a Baptist and a Buddhist as roommates.
A common noun is a noun referring to a person, place, or thing in a general sense -- usually, you should write it with a capital letter only when it begins a sentence. A common noun is the opposite of a proper noun.
All the gardens in the neighborhood were invaded by beetles this summer.
A concrete noun is a noun which names anything (or anyone) that you can perceive through your physical senses: touch, sight, taste, hearing, or smell. A concrete noun is the opposite of a abstract noun.
Whenever they take the dog to the beach, it spends hours chasing waves.
An abstract noun is a noun which names anything which you cannot perceive through your five physical senses, and is the opposite of a concrete noun.
Justice often seems to slip out of our grasp.
A countable noun (or count noun) is a noun with both a singular and a plural form, and it names anything (or anyone) that you can count.
Miriam found six silver dollars in the toe of a sock.
A non-countable noun (or mass noun) is a noun which does not have a plural form, and which refers to something that you could (or would) not usually count.
The furniture is heaped in the middle of the room.
A collective noun is a noun naming a group of things, animals, or persons. You could count the individual members of the group, but you usually think of the group as a whole is generally as one unit.
The class was startled by the bursting light bulb.
I bet you never knew there were so many kinds of nouns. Think you've go it? How about a quiz? Try this one from Interlink Language Centers.