The best way to learn DevOps is by joining a training class or program. This way you not only understand the concepts of DevOps but also gain industrial exposure, which is very necessary to get better opportunities once the training gets over. I wouldn't suggest you take up so-called free online courses, as they will only scrape the surface of DevOps, which in itself is a huge domain.
To master DevOps, you must be an expert in tools for different aspects of DevOps like CI/CD pipeline, Continuous Monitoring, infrastructure configuration, feedback loop, etc.
Let me share a feedback video of one of our happy learners who enrolled in this DevOps course and has successfully upskilled his career. Do check out this video to get a better understanding.