Workflow syntax
The workflow file is written in YAML. In the YAML workflow file, you can use expression syntax to evaluate contextual information, literals, operators, and functions. Contextual information includes workflow, environment variables, secrets, and the events that triggered the workflow. When you use run in a workflow step to run shell commands, you can use specific workflow command syntax to set environment variables, set output parameters for subsequent steps, and set error or debug messages.
Events
You can configure workflows to run when specific GitHub events occur, at a scheduled time, manually, or when events outside of GitHub occur.
Authentication and secrets
GitHub provides a token that you can use to authenticate on behalf of GitHub Actions. You can also store sensitive information as a secret in your organization, repository, or environments. GitHub encrypts all secrets.
Environments
Workflow jobs can reference environments that have protection rules or environment-specific secrets.
GitHub-hosted runners
GitHub offers hosted virtual machines to run workflows. The virtual machine contains an environment with tools, packages, and environment variables for GitHub Actions to use.
Administration
When you run workflows on GitHub-hosted runners, there are usage limits and potential usage charges. You can also disable or restrict the usage of GitHub Actions in a repository and organization.