Google provides a service called Custom Search which can be used to add search functionality to search your own website. That is, you can place a search bar in your website that your users can use to search only the content of your website using Google's search engine.
<script async src="https://cse.google.com/cse.js?cx=blahblahblahblahblah:blahblah"></script> <div class="gcse-search"></div>
scriptpart into the
headsection of your HTML webpage. Copy the
divpart into whereever you want the search bar in the
bodysection of your HTML webpage. Your webpages should now have a Google Custom Search bar displayed where you placed it.