Reliable Resources: If it's on the internet, it has to be true?

Agile and Scrum are frameworks with a broad range of options but also some pretty hard guardrails.

With the best of intentions, some will espouse their ideas/agenda as solid agile, but I'd recommend sticking to the core reliable sources, and look at anything outside of that circle with a critical eye to make sure they are sticking closely to the principles of Agility.

To that end, here's a few reliable resources.

Reliable Scrum Resources:

Scrum Alliance:  www.scrumalliance.org (Mike Cohn - where the most recognized certifications (CSM, CSP, CTP, etc.) come from)
Agile Manifesto:  www.agilemanifesto.org (Where it all started)
Agile in a Nutshell One Pager:  http://blog.crisp.se/wp-content/uploads/2016/10/Agile-poster-2016-ver14.pdf
Scrum Inc:  https://www.scruminc.com/ (Jeff Sutherland co-inventor of Scrum)
Version One:  https://www.versionone.com/
Rally:  https://www.ca.com/us/why-ca/about-us/acquisitions/rally-is-now-ca-technologies.html?cid=GLOB-EOA-ABUS-ADB-000083-00000151
Ken Schwaber:  https://kenschwaber.wordpress.com/
Robert "Uncle Bob" Martin the "clean coder":  https://sites.google.com/site/unclebobconsultingllc/

This is most certainly not an exhaustive list, but it should give you a good start and anytime you hear anything that's not covered here, or even worse, contradicts the spirit of what is on these sites is suspect to say the least.