GitHub Actions is a CI/CD platform built into GitHub. Workflows are YAML files that define triggers, jobs, and steps - each step runs a shell command or a reusable action.

Common uses: run tests on every push, lint code on PRs, build and publish Docker images on release tags, and deploy to staging on merge to main. Actions can be scoped to push, pull_request, schedule, or manual dispatch triggers. Self-hosted runners allow custom hardware or private network access.