It is a text file with a single column of URLs you want to find the keywords in. If you do not have a list of urls, you can always generate it from the website's sitemap. You will typically find the sitemap at www.websitename.com/sitemap.xml. Here is a sample file you can use to get started.
Keywords and phrases are converted to their root forms. Common articles such as "of", "the", and "at" are removed. We then search for these root words within the same sentence. This helps with SEO to find opportunities to link to other pages.