JSTOR contains a range of types of sources including books, images, articles, primary sources, and more. If you want to narrow your results to a specific type of source, there are a couple ways you can do this.
In Advanced Search
You are able to use the "narrow your results" option in the advanced search area. This can be especially helpful when trying to eliminate reviews that appear in journals in your result list.

On the Results Page
On the results page, you have several different options for limiting your content.
Academic Content: You can limit to results published in Journals versus Book Chapters
Primary Source Content: If you are searching for primary sources, you can limit by the type of primary source you are looking for: serials, documents, or books.
Date: You can limit your search results to a specific publication time frame or to help you find more recent research.
Subject: Limiting by subject can be especially helpful when you are trying to find research from a specific perspective. For example, if you are looking for literary research on Jane Austen, you might want to limit by subject to "Language and Literature." Alternatively, if you wanted results related to Jane Austen and her influence on women, you might want to limit by subject to "Feminist and Women's Studies.