Search engines scan the web by an algorithm called spiders and the information if on there web and the spider travels through the web.The search index is a database which is a information organised.This is why google is the best search engine because of its algorithms
and its software.
The algorithms will check if the search has a title of the web page. If the web page has the same words or in the same order as the search then that means that the search has been requested
The difference is that the web browser connects to the internet that you need and the search engine is something that you need to search when you need help
They use the HTTPS (hyper text protocol secure) to stop scammers from looking on the higher ranking algorithms