Link text is the visible text inside a link. This text tells users and Google something about the page you're linking to. Links on your page may be internal—pointing to other pages on your site—or external—leading to content on other sites. In either of these cases, the better your anchor text is, the easier it is for users to navigate and for Google to understand what the page you're linking to is about.
I would focus on building your personal brand online and building a website right away that you can use as a testing ground for learning digital marketing skills. Most digital marketing programs are too theoretical and digital marketing is a fast evolving industries so you need to be constantly learning through active experimentation to become good enough to consistently make money.
Website saturation and popularity, or how much presence a website has on search engines, can be analyzed through the number of pages of the site that are indexed by search engines (saturation) and how many backlinks the site has (popularity). It requires pages to contain keywords people are looking for and ensure that they rank high enough in search engine rankings. Most search engines include some form of link popularity in their ranking algorithms. The following are major tools measuring various aspects of saturation and link popularity: Link Popularity, Top 10 Google Analysis, and Marketleap's Link Popularity and Search Engine Saturation.
The leading search engines, such as Google, Bing and Yahoo!, use crawlers to find pages for their algorithmic search results. Pages that are linked from other search engine indexed pages do not need to be submitted because they are found automatically. The Yahoo! Directory and DMOZ, two major directories which closed in 2014 and 2017 respectively, both required manual submission and human editorial review. Google offers Google Search Console, for which an XML Sitemap feed can be created and submitted for free to ensure that all pages are found, especially pages that are not discoverable by automatically following links in addition to their URL submission console. Yahoo! formerly operated a paid submission service that guaranteed crawling for a cost per click; however, this practice was discontinued in 2009.
Webmasters and content providers began optimizing websites for search engines in the mid-1990s, as the first search engines were cataloging the early Web. Initially, all webmasters only needed to submit the address of a page, or URL, to the various engines which would send a "spider" to "crawl" that page, extract links to other pages from it, and return information found on the page to be indexed. The process involves a search engine spider downloading a page and storing it on the search engine's own server. A second program, known as an indexer, extracts information about the page, such as the words it contains, where they are located, and any weight for specific words, as well as all links the page contains. All of this information is then placed into a scheduler for crawling at a later date.