Developers can use CircleCI to create containerized continuous integration (CI) environments by combining images like building blocks, thanks to its native support for Docker. This guide explains how to build a Docker image in CircleCI and push it to Docker Hub, a cloud-based Docker image registry. It outlines the necessary prerequisites, such as accounts on CircleCI, GitHub, and Docker Hub, and provides a detailed overview of setting up pipeline configurations, including defining jobs, setting up remote Docker with layer caching, and using Docker Compose for testing. By automating the build, test, and deploy workflow for Docker images with CircleCI, developers can achieve faster build times and consistent deployments. The process includes checking out source code, setting up Docker environments, running tests, building Docker images, and pushing them to Docker Hub using authentication credentials managed as environment variables. CircleCI offers two approaches to build Docker images: a dedicated virtual machine with a machine executor or a remote Docker engine with a Docker executor, both optimizing the CI/CD pipeline for efficiency and reliability.