A thesis statement tells the reader what the paper is about. It is generally 1-2 sentences long and appears in the beginning portion of the essay, usually at the end of the first paragraph. 

A thesis statement...

1. Introduces the main topic or argument.
2. Provides the reader with a guide to help interpret or understand the subject. 
3. Tells the reader what to expect in the essay.
4. Give your writing direction and focus.
5. Is one of the most important parts of your writing. 

What kind of essay needs a thesis statement?

Every essay, from argumentative to narrative, benefits from a thesis statement. The thesis is the guide that will help your reader understand everything that is to come. Even the most thought-out essays can be hard for a reader to follow without one.