In writing an essay, you have to assume the reader (even if it is your teacher) is not familiar with the topic or work (novel, poem, play, etc.) you will be exploring. The purpose of Background Information, usually 2 to 4 sentences, is to give the reader vital information to understand the main idea / topic / theme of your essay and the basic context of the referenced work (novel, poem, play, etc.).

It is important to think about the following when creating Background Information:

Who – who wrote the work? who are the main characters?

What – what is the plot (story) of the work?

Where – where does the story take place?

When – when was the work written? when does the story take place?

Why – why is the work or topic important? why was the work written?

The information you provide depends on the idea / topic / theme and purpose of your essay. You will not always need to answer all of the above background questions. 

Example

If you are writing an essay about what makes Santiago a good example of a role model in The Old Man and the Sea:

A role model is a person looked up to by others as an example to be imitated and inspired by. Manolin, the young man in The Old Man and the Sea, is fortunate to be positively influenced by Santiago, the main character in the novella. Ernest Hemingway’s (who) 1951 (when) story reinvigorated his career (why) and follows a veteran fisherman, Santiago, (who) from Cuba (where) who has been unable to catch a fish for 84 days. He is finally able to catch and kill a marlin but eventually loses the fish to ravenous sharks (what).