Honestly, there's too many ways to do gitOps, and it's kind of overwhelming. Weave Flux is the most mature, so just start there. https://www.katacoda.com/courses/weave/flux-training If you pay WeaveWorks for Flux, everything is pretty magical, but if you have $0, then start with https://github.com/justinbarrick/flux-operator and https://github.com/justinbarrick/fluxcloud which do an ok job. When you get to secrets, use https://github.com/bitnami-labs/sealed-secrets
If you like helm, then maybe consider https://github.com/giantswarm/chart-operator or https://github.com/stefanprodan/gitops-helm
Oh, I did remember this training too: https://github.com/weaveworks/flux/blob/master/site/helm-get-started.md