As a writer, you use a quotation to examine the connection between the use of language and a text's larger themes. In other words, a quotation introduces a linguistic argument, an argument in which you will show how form contributes to content, how the author's use of language supports your thesis.
Normally, quotations are followed by your commentary, a discussion in which you teach the reader the significance (vis-à-vis your thesis) of the quoted passage's tone, diction, word choice, imagery, syntax, etc.
Remember that quotations do not speak for themselves: a quotation followed by no or insufficient commentary makes no sense in the essay; the reader does not know why it is there.
EXAMPLE: Let us suppose that you are writing an essay on Shakespeare's Macbeth. Your thesis involves an assertion that Macbeth's evil brings about a self-knowledge whereby he is more keenly aware of the consequences of his crimes as his crimes become worse and worse. You choose the following quotation to support your argument:
that which should accompany old age,
As honor, love, obedience, troops of friends,
I must not look to have.
Your task now is to show how Shakespeare's use of language supports the thesis. You might want to mention that Macbeth is here viewing his crimes in light of his relationships with others. Earlier his soliloquies have largely concerned only his relationship with his own soul: words like honor, love, and obedience imply relationships outside of the self, as the word accompany more explicitly signifies relationship. You might want to point out how troops is ironic, as hostile troops are now assembling outside Macbeth's castle. The word must implies a kind of imperative, a suggestion that Macbeth's crimes have gradually taken from him any option of choice. These ideas are only a few ways to talk about the use of language in the passage. You could also talk about the syntax (how Macbeth puts the main clause, with his own personal pronoun, at the end of the sentence), the notion of expectation and knowledge ("I must not look to have" instead of the simpler "I cannot have" or "I must not have").
FORMAT: Remember that poetry, unlike prose, is written in lines. If you are quoting two lines or less of poetry, keep the quotation within quotation marks in your own margins, making sure to signify line breaks with a spaced slash. More than two lines of poetry should be indented ten spaces, single-spaced, without quotation marks, preserving the poetic lines (see Macbeth quotation above). The same general rule applies to prose passages, except, of course, there is no need for the slashes or line breaks.
TWO LINES OR LESS OF POETRY INTRODUCED WITH MAIN CLAUSE:
Antony's funeral speech immediately commends the attention of the crowd: "Friends, Romans, Countrymen, lend me your ears; / I come to bury Caesar" (III. 73-4).
Remember that a comma precedes the quotation if that quotation completes the clause that introduces it.
MORE THAN TWO LINES OF POETRY COMPLETING A CLAUSE:
Antony subtly undermines Brutus' reputation when he suggests that,
The noble Brutus
Hath told you Caesar was ambitious.
If it were so, it was a grievous fault,
And grievously hath Caesar answered it.
Notice how the lines of the quotation stop where the poetic line stops. the indented quotation uses no quotation marks.
In Elizabethan drama, citations are normally made with Act (large Roman numerals), scene (small Roman numerals), and line (Arabic numerals: separated by periods (no spaces). When quoting novels or other works in which lines are not numbered, cite with the page number (using "p" is unnecessary) in parentheses, followed by the terminal punctuation. EXAMPLE: Ed appears to be smugly aware that he has been living a life of "antifriction" (55).
Place citation at the end of sentences, even if you use a quotation at the beginning of a sentence. EXAMPLE: Living a life of "antifriction," Ed seems nevertheless eager to meet whatever challenge Lewis puts to him (55).
Make sure to give a quotation in its context. Let there be no doubt where the quotation has come from and why it is in this part of the essay.
Finally, quotation is a noun. Do not use quote (a verb in formal English) when you mean quotation.