This document provides an introduction to search engines and related concepts. It defines a search engine as software that systematically searches the web. It explains that a search engine results page (SERP) is the page returned by a search engine in response to a user's query. It also describes how search engines work through crawling, indexing, and ranking webpages. It then discusses different types of search engines, domains, web hosting, URLs, and how to identify niche target audiences for digital marketing.