Docker packages an application, with everything it needs to run, into a container image that behaves the same on a laptop, a test server and in production. DevOps is the wider set of practices around it: automated pipelines, infrastructure as code, monitoring and shared ownership of running software.
Teams invest in containers and DevOps to take the friction and risk out of releasing software. The goal isn’t more tooling; it’s fewer manual steps, faster feedback and the confidence to deploy whenever a change is ready.