Setting up a robust Drupal internal site search that searches all of the content that you add to a complex site can be a bit like finding your way through a maze.
Drupal 8 core Search has been revamped and is much more powerful and accurate than in D7, but it still concentrates on text in nodes and not other entities those nodes might contain—like Paragraphs, Views, or custom blocks. Core Search also does not allow you to choose which fields you want to index, how important those fields are, or use any preprocessors to tailor your search. Search API gives you all this and more.
Search API is a Drupal contributed module that allows you create searches on any entity known to Drupal. You can use Views to create a custom search results page with specific filters. You can create different indexes tied to specific sections or content on your site. You can do just about anything to architect your search experience other than use the core Search block—which is really the only thing that makes core Search worth using. This post however, will show you how to take advantage of the power of Search API, and keep your site search box.