What is SEO?
Imagine you are a fashion website. When someone searches for a phrase related to your business - like women's vintage dresses - Google will present them with a list of search engine results that are most relevant to the phrase entered into the search box.
So, in other words, think of Google and SEO as like a matchmaker: its algorithm goes through your website and, based on the prominent phrases it finds, ranks your website accordingly.
Google essentially wants to match what customers type in with the most accurate result. If your website heavily features women's vintage dresses, therefore, your items are more likely to be found by people typing women's vintage dresses into Google.