Great question and a very important topic!
I suggest starting with the
OWASP DevSecOps Guideline. It lays out and explains many things, from an introduction to DevSecOps to a maturity model to what is known as 'Shift Left' security. The same project also has a
document repository on GitHub.
Beyond that, I suggest looking at resources from vendors that you trust or work with. For example,
I'm a fan of Cloudflare.
AWS and
Google each offer guidance and skills training for DevSecOps in their environment