GitHub Actions is an event-driven automation tool that leverages temporary virtual machines to execute shell commands on your repository. This is not a simple tutorial but a mental model explaining how GitHub Actions actually functions. At its core, GitHub Actions uses temporary virtual machines that run shell commands triggered by specific events, such as a code push or pull request.

There is no background daemon or always-on server; everything runs on demand when an event occurs. When a developer pushes code, GitHub receives the push, scans the `.github/workflows/*.yml` files, identifies the relevant workflows, and starts a fresh virtual machine. This VM clones the repository, runs the defined steps, and then destroys itself.

Each run is isolated, temporary, and stateless, ensuring no residual data from previous runs. The environment for these actions is typically a brand-new Ubuntu Linux VM that includes essential tools like Bash, Git, and Unix utilities. This VM is ephemeral, living only for the duration of the job.

All shell commands run inside this VM, at the repository's root, and follow standard Linux path conventions. Understanding this model is crucial for developers. It demystifies the process, showing that GitHub Actions is not magic but a pragmatic use of virtual machines and shell scripting.

This knowledge is valuable for automating tasks like testing, builds, and deployments, which are fundamental in modern software development practices.