What is a fundamental symbol in "The Lottery" by Shirley Jackson?

The black box is indeed the main symbol.  It represents tradition.  The villagers are not sure about the box's history.  They recall a chant and a certain handshake that used to go with it.  Indeed the original box is tattered and worn, barely  holding together.  They did make some modifications, replacing wood chips with slips of paper as the villages population grew.  The only thing they are really certain about is the use of rocks.

The Lottery, like the box, is shrouded in mystery.  No one really knows why they conduct it (other than Old Man Warner making a reference to it having to do with good corn crops in June).  They just follow along because it has always been done. 

There has been talk of getting rid of the lottery, indeed some towns already have, and there seems to be some talk among the young people of junking the lottery.  In this way the lottery is like the box.  It is barely clinging together.  But just as the villagers pull the box out once a year and go through the proceedings, observing what ceremonies and protocols they remember, they still obediently observe the lottery.

What is revealed when Buck licks Thornton's hand in "The Call of the Wild"?

Buck has gone through a horrible series of events by the time he ends up with Thornton.  He has had masters that he could trust, and he has had ones that were horrible beyond belief.  When Thornton arrived on the scene and saved Buck from being beaten to death by the woman, her husband, and her brother, Buck realizes that he has "landed on his feet," so to speak.  When Buck licks Thornton's hand, he is letting him know (and us, the readers) that he trusts him and believes in him, and even that he will lay his life down to defend him.

Check the links below for more information on these characters!  Good luck!

In Act II, Scene 4 of Romeo and Juliet what does Tybalt send to Romeo's house?

You can find the answer to this right at the very beginning of the scene.

Benvolio and Mercutio are together walking on a street.  Benvolio tells Mercutio that Tybalt, who is a relative of Juliet, has sent a letter to Romeo's house.  In the letter, he is challenging Romeo to fight a duel with him.

Mercutio and Benvolio are worried about this because Tybalt is a very good fencer.  They are afraid he will kill Romeo.

When Romeo shows up in the scene, they stop talking about this and start teasing him about Rosaline.  They still have no idea what is going on with him and Juliet.

In "Of Mice and Men," by John Steinbeck is the character George a hero or villain. Why?

In Steinbeck's novella, "Of Mice and Men," there do not seem to be any heroes;  George is closer to the anti-hero than a real hero since he is contrary to the archetypal hero.  For, he reluctantly cares for Lennie:

I could get along so easy and so nice if I didn't have you on my tail.  I could live so easy and maybe have a girl....You keep me in hot water all the time.

While George complains of the burden of caring for Lennie, he tells others that he promised Lennie's aunt that he would look out for him, understanding that Lennie cannot care for himself. Under these circumstances, George draws the sympathy of the reader.

Likewise, George elicits sympathy again from the reader when he worries about Lennie's fate if he is arrested for killing Curley's wife; George realizes that Lennie will be terrified and lonely if has to live in an asylum or prison.  So, in an act that is not typically heroic, George spares Lennie his fate.  Slim, the mule driver who has "God-like eyes" tells George,

'You hadda, George.  I swear you hadda. Come on with me.'

Not all people will recognize George's act as heroic--in fact, he may be arrested if found out by the law--but some of the men at the ranch house will understand that George has protected Lennie as Slim has done, thus arousing their sympathy.  For this reason, George more closely fits the profile of the anti-hero in literature than he does the archetypal hero.

What is the importance of the reference of Jephthah?

The reference to Jephthah in "Hamlet" is by Hamlet to Polonius. In this scene hamlet is outwitting Polonius using many literary illusions, this one being biblical.

In the bible Jephthah prays for the help of god to win in battle, and in return, he offers the first person to walk through his door as a sacrifice. He believed that most likely it would be a servant... However, it turned out to be his virginal daughter.  Jephthah's daughter sacrifices herself, telling her father that she will honour his promise to god, and dedicates her life to work in the temple. 

Jephthah did not want to sacrifice something of actual value, like his daughter. Polonius is self seeking at best, wanting his daughter for what he can use her for. He was happy to have her engaged to Prince hamlet, but happier still to have her used to test whether or not he was mad. 

Ophelia ends up making the sacrifice of her own love by testing Hamlet, in the "get thee to a nunnery" scene, causing her to go mad, and ultimately kill herself. 

To call Polonius Jephthah is to insult his integrity, as well as foreshadowing his own lack of heirs, as Ophelia dies childless, and Laertes also in the final scene.

Who is the only person that understands why He killed Lennie? and Why?In Chapter 6

At the end of the novel, Slim and George are left together. Slim utters a very simple phrase, "you hadda." We can interpret this to mean that Slim said that George had to do this. Slim understood that if George had not killed Lennie, Curley was going to. Curley would have made Lennie suffer, his rage over his wife's death was very strong, and legitimately so.

Slim's words were almost unspoken, but the gesture of understanding was something George desperately needed after killing his best friend out of compassion. Few people have the power to do such a thing, and Slim recognized this in George and gave him credit for it by just being there.

What is the thesis of "The Story of an Hour"?

Being a fictional short story, there isn't an actual thesis in the work.  If I were going to choose one sentence that emphasizes the meaning of the story it would be the very last sentence.  

When the doctors came they said she had died of heart disease--of joy that kills.

This sentence points to the irony in the story.  We as readers know that Mrs. Mallard didn't die joyfully, but rather at the shock and disappointment that her husband was still alive.

If you are looking for a thesis, as in the main point, of the story, it would be that women are oppressed in marriage relationships.  In most of her works, Chopin was concerned about showing the role of women in society and in marriages.