Indexing: Post-crawling content the Spider stores the indexed page in a giant database from where those can be retrieved upon entering a related search string or keyword. For humans this will not be possible, but for search engine, this is every day’s work. Sometimes, the search engines cannot understand the page content. And for that, you need to correctly optimize the page.
Yoast - a very useful and FREE (or freemium) WordPress plugin which analyses page copy in a traffic light signal basis for how SEO friendly the copy is based on keyword density, alt-attributes, SEO titles and Meta descriptions, slug etc. It cannot guarantee ranking, as it in no way affects search engine algorithms, but gives a great estimate of how well your copy is written based on your keyword. This is great to use as a guided SEO editor whilst you write and makes you aware of key on-page SEO techniques you should be utilizing.