What does it mean when it asks, "Briefly summarize the plot of 'The Most Dangerous Game.' This is not an overall plot summary but a summary of the essence of the plot."
Most likely what your teacher is looking for here is a brief summary of the plot to the story “The Most Dangerous Game.” When a teacher asks for the “essence” of something they want their students to discuss the most important aspect of it. In other words, don’t give dozens of details, give the main idea and a few supporting points.
Since we usually teach plot as a four or five part structure, your teacher might not want you to address each part on its own (in other words, don’t say “these things happen in the basic situation, these in the rising action, these in the climax, these in the falling action, and finally these in the resolution.”)
For the story “The Most Dangerous Game” you might start by writing, “A man finds himself shipwrecked on an island inhabited by a famous hunter. Unknown to him, the hunter plans on setting the man loose in the jungle and then hunting him down.” A few more lines about what happens next should communicate the “essence” of the plot.
The other questions that you asked should be submitted as individual questions.