Nouns

Nouns represent person place or thing, including abstractions.  Nelson Mandela, book, compost, humor, confusion, exasperation are nouns.  There are a potentially infinite number of nouns as new ones are being invented all the time.  English nouns are inflected (changed in form or declined) only to show plural and possessive qualities.  "Book" becomes "books" in plural and "book's" would indicate possession as in "the book's jacket."

Only proper nouns, the name of a place or person, are capitalized: Ferdinand, Severus, Rupert, Sir Thomas Crapper, etc.    

Pronouns

Pronouns take the place of nouns.  There are only a few of these and you already know them all.  Who (whom in object case), what, which, that, each, are examples of general pronouns.  Apart from who, whose object form is whom and possessive is whose, only the personal pronouns are declined extensively.  Declension is used to indicate subject, object, or possessive case according to how they are used in the sentence and depending upon the number, person, and gender of the noun represented by the pronoun.  Here is a chart.    

Personal Pronoun Declension

number	person	gender*	Cases of Personal Pronouns				possessive adjectives
			subject	object	possessive	reflexive
singular	1st	m/f	I	me	mine	myself	my
	2nd	m/f	you	you	yours	yourself	your
	3rd	m	he	him	his	himself	his
		f	she	her	hers	herself	her
		n	it	it	its	itself	its
plural	1st	m/f	we	us	ours	ourselves	our
	2nd	m/f	you	you	yours	yourselves	your
	3rd	m/f/n	they	them	theirs	themselves	their

* m=masculine f=feminine n=neuter

For further practice, see Common Errors: troubles with case