I find search engines as one of the most amazing software created out there. I found the links below helpful in learning the theoretical underpinnings.
The Fundamentals and theory
Information Retrieval and Mining Massive Datasets: An excellent udemy course on learning the basics of search engines. Does an excellent job of going from basics to advanced.
Introduction to Information retrieval slides: A good resource if you want to swift through the basics quickly in the form of slides.
- You can experiment with an easy setup and powerful open-source search solution ElasticSearch its related tools.