There are two types of links; internal and external. Internal links direct the reader to another page within a website, and external links direct a reader to a page on a different website. In short, backlinks are extrenal links that direct the reader to another source of information; links can also be referred to as a hyperlink. When a website uses an external link, it becomes a backlink to the page it is referring the reader to. Search engines, such as Google, use backlinks as a way to validate, or confirm, that a site has valuable content. As part of Google's algorithm, the more backlinks a site has the higher value that site will get in the search results because it is perceived that more backlinks means the site is more valuable.
To the reader, they typically see a different color in the text of an article they are reading. The text is how that url/link gets registered in the search engines; the words associated with the url tells the search engines "this is the content related to this url." These would be keywords associated with that url and often there is a relationship between the words associated with a url and the content on the particular page that is getting a backlink.
If you have a blog or website, you may want to link some of your words to a page that is not within your website, to do this you would do the following:
Go to your HTML script, then a backlink (external link) is written in the following way-
<a href="http://www.example.com" rel="dofollow">example backlink</a>
If it is a specific page, you could just copy the URL of the page you are linking to and replace the "http://www.example.com" with that URL.
There are different types of backlinks; rel="dofollow", rel="nofollow", and rel="noopener noreferrer." A "dofollow" tells the search engines that they want the search engines to recognize the link and that it has value. A "nofollow" tells the search engines not to place value on the link. A "noopener noreferrer" masks the source of the link, and shows as a direct link rather than reflecting the actual source of the traffic.