The introduction introduces the subject. This may include a short overview of current research status, or a summary of controverse positions of different authors.
You can start the introduction with a quotation, with an interesting fact, or with an explanation of a term relevant to your essay.
What's most important is to introduce your thesis.
By the way, you needn't write your introduction first. Some people prefer launching right into the subject, and write the introduction afterwards, and so do I.
See also here Introduction