First, mood and tone aren't the same thing. It's common that teachers lump those two items together because they do come hand in hand quite often. Additionally, tone will often affect mood, so many readers assume that they are equivalent.
In a nutshell, tone is more about the author or speaker of a piece, and mood is more about the reader. Tone refers to an author's or speaker's use of words and writing style to convey his or her attitude toward a topic. Tone could be defined as how/what the author feels about their subject. What the reader feels is known as the mood.
I'll start with tone for this poem. When the poem starts out, I feel that the speaker's tone is a mixture of solemn, nostalgic, and perhaps even distracted. The poem begins late at night with the speaker trying to find some way to take his mind off the lost Lenore. He's very sad about losing his loved one, and he can't stop thinking about her.
Eagerly I wished the morrow;—vainly I had sought to borrowFrom my books surcease of sorrow—sorrow for the lost Lenore—For the rare and radiant maiden whom the angels name Lenore—Nameless here for evermore.
That I scarce was sure I heard you”—here I opened wide the door;—Darkness there and nothing more.
Much I marvelled this ungainly fowl to hear discourse so plainly,
“Be that word our sign of parting, bird or fiend!” I shrieked, upstarting—“Get thee back into the tempest and the Night’s Plutonian shore!Leave no black plume as a token of that lie thy soul hath spoken!Leave my loneliness unbroken!—quit the bust above my door!Take thy beak from out my heart, and take thy form from off my door!”
And my soul from out that shadow that lies floating on the floorShall be lifted—nevermore!
Poe's poem "The Raven" starts with these lines:
Once upon a midnight dreary,
while I pondered, weak and weary...
Note that the words "dreary" and "weary" introduce the mood of darkness and lethargy. Poe's diction, or word choice, serves to promote and deepen the mood as seen in the second stanza, which refers to "bleak December," "dying embers" that make "ghost" shadows on the floor, and the narrator's vain attempt to find relief from his sorrow "for the lost Lenore."
The rustling of the curtain fills the reader with "fantastic terrors never felt before." There is an incessant tapping at the door that reveals, when opened, only darkness. As the poem continues, it is apparent that this is quite simply a poem about the speaker's dead love Lenore. Even the bird in the story's title supports the mood: the raven is black (the color of death) and is an animal often associated with death. Repeated references to the presence of the raven sustains the mood Poe creates and develops throughout the poem.
The raven thus becomes “emblematical of Mournful and Never-Ending Remembrance.”
Poe's repeated images of sadness and loss and the symbolism associated with the raven emphasize the feeling of melancholy. The poem comes full circle with the narrator's resignation to Lenore's loss, and his knowledge that his depression and misery will never leave him because he will never recover from his loss.