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

  1. 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.

  2. Introduction to Information retrieval slides: A good resource if you want to swift through the basics quickly in the form of slides.

Practice

  1. You can experiment with an easy setup and powerful open-source search solution ElasticSearch its related tools.