It's hard for me to tell you what to put in your introduction and conclusion without knowing what you've expressed in the body of your work. The good news is that you know what you've expressed, and you should therefore not have too much trouble making an introduction and conclusion.
The purpose of your introduction is--SURPRISE!--to introduce the main idea of your work. What is your main idea: that The Scarlet Letter is the greatest book ever written?; the worst? a fascinating study of hypocrisy? a wonderful glimpse into Puritan society?
Whatever your main idea is, that's what you want to state in your introduction. Do not get involved in the details--that's for the body of your work. To make your introduction interesting, you might want to begin with a question, with a quotation, or with a personal story.
As for the conclusion, its main purpose is simply to restate what was said in the introduction. The conclusion might be the place to be a little more opinionated, or to give the reader something to think about. Still, your main purpose is to hammer home your main idea one last time.