https://www.google.com/advanced_search

https://ahrefs.com/blog/google-advanced-search-operators/

Start with these

Librarians at some university libraries will teach/assist you in how to better use search resources.

OSINT - Open Source Intelligence

https://en.wikipedia.org/wiki/Open-source_intelligence

I don’t know of any such resource. When I want to find stuff I use the light switch on the back of my skull to switch off my brain and ask HN to come up with answers for me. To my knowledge there is no way to search through internet documents or generate answers to questions using any form of known “conversational synthetic knowledge” technology.