GitHub: What It Is, Features, and How It Works

What is GitHub?

GitHub is a web service for storing and collaborating on Git repositories, founded in 2008 by Tom Preston-Werner, Chris Wanstrath, and PJ Hyett. In 2018, the company was acquired by Microsoft for $7.5 billion. The platform provides a web interface for all Git operations, adding social features on top: forks, stars, subscriptions, code review, and a built-in continuous integration system.

The key difference between GitHub and its competitors is its open ecosystem and the largest developer community. GitHub hosts the source code for Android, Kubernetes, React, Swift, Kotlin, and thousands of other open-source projects. This makes the platform not just a code storage tool but also a social network for developers: you can follow projects, discuss changes, and contribute through pull requests.

According to a Microsoft report (2024), more than 10 million new Pull Requests pass through GitHub daily, and the number of monthly active users has exceeded 100 million. The platform supports over 500 programming languages, automatic language detection by file extension, and code syntax highlighting.

Key Features of GitHub

GitHub's functionality goes far beyond simple Git hosting. The platform provides: GitHub Actions — a built-in CI/CD system; GitHub Packages — a registry for packages and containers; GitHub Codespaces — cloud development environments based on VS Code; GitHub Discussions — a forum for the community; GitHub Security — Dependabot for automatic dependency updates and vulnerability scanning; GitHub Copilot — an AI assistant for writing code.

For organizations, GitHub offers GitHub Enterprise — an enterprise version with self-hosted (GitHub Enterprise Server) or cloud deployment (GitHub Enterprise Cloud). Enterprise features include SAML/SSO authentication, audit logging, repository security policies, and 99.95% availability SLA. The Enterprise version is used by companies such as Google, Apple, and Airbnb.

An important feature of GitHub is GitHub CLI (gh), which allows you to perform all platform operations from the command line without using the web interface. With gh, you can create repositories, manage Issues, review Pull Requests, and run Actions directly from the terminal, speeding up work for developers accustomed to the command line.

Pull Request and Code Review

Pull Request (PR) is the main mechanism for making changes to a project on GitHub. A developer creates a branch with changes, publishes it on GitHub, and sends a merge request (Pull Request) to the main branch. Other project participants see the diff between branches, can leave comments on specific code lines, suggest changes, and approve or reject the request.

The code review process on GitHub is built around PRs. Each comment is attached to a specific line in the diff and can be of three types: Comment (regular comment), Request Changes (requires fixes), and Approve (approval). After making changes, the author updates the PR with a new commit, and the review process repeats. Once all issues are resolved and the PR is approved, the changes are merged into the target branch.

# Creating a feature branch and pushing
git checkout -b fix-login-bug
git add src/
git commit -m "Fix login validation error"
git push -u origin fix-login-bug

# Creating a PR via CLI
gh pr create --base main --title "Fix login validation" \
    --body "Fixed edge case with empty email field"

# Viewing and merging a PR
gh pr review --approve fix-login-bug
gh pr merge --squash fix-login-bug

GitHub supports branch protection rules: you can prevent direct pushes to main, require a mandatory number of approvals before merging, run Actions checks, and require the branch to be up to date before merging. Branch protection is configured in Settings → Branches and is a mandatory practice for production projects, preventing accidental introduction of unstable code into the main branch.

GitHub Actions and CI/CD

GitHub Actions is a built-in CI/CD platform that allows you to automate workflows directly in the repository. Workflows are described in YAML files located in the .github/workflows/ directory. Each workflow consists of one or more jobs that run on runners — virtual machines with Linux, Windows, or macOS.

Actions supports an event-driven model: workflows are triggered on push, PR creation, release publication, on a schedule, or via webhook. This allows you to automate building, running tests, static code analysis, publishing to app stores, and deploying to a server without developer involvement. Below is an example workflow for an Android project:

name: Android CI

on:
  pull_request:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Set up JDK 17
        uses: actions/setup-java@v4
        with:
          java-version: '17'
      - name: Build with Gradle
        run: ./gradlew assembleDebug

The Actions ecosystem includes over 20,000 ready-made actions in the GitHub Marketplace. Popular actions: checkout (clone repository), setup-java/setup-node/setup-python (environment setup), upload-artifact (save build artifacts), cache (dependency caching for speed), slack-notify (send Slack notifications). Actions also supports matrix builds — simultaneous execution on multiple OS or language versions.

GitHub Projects and Issues

Issues is a built-in task tracking system on GitHub. Each Issue has a title, description, labels, assignees, milestones, and linked Pull Requests. Issues can be templated — different templates are used for bug reports, feature requests, or questions, which are automatically inserted when creating.

GitHub Projects (formerly Projects Beta) is a project management tool based on boards, similar to Jira and Trello. Projects supports custom fields (status, priority, sprint), linking with Issues and Pull Requests, automating card movement when task status changes, and analytics in the form of a burndown chart. Projects is available in two modes: Table (table view) and Board (kanban board).

For release management, GitHub provides Milestones — groups of Issues and PRs united by a common goal with a deadline. Each milestone shows progress: how many tasks are open, how many are closed, and whether the deadline is being met. Milestones integrate with Releases — when publishing a release, you can link it to a milestone and automatically generate a CHANGELOG based on closed Issues.

GitHub Pages and Wiki

GitHub Pages is free hosting for static sites that automatically publishes repository content at https://username.github.io/repository. Pages supports HTML, CSS, JavaScript and static generators: Jekyll (built-in), Hugo, Next.js (export), and MkDocs. Configuration includes choosing the branch and directory for publication, as well as custom domain support.

For technical documentation, GitHub provides Wiki — a built-in wiki system that is also stored as a Git repository. Wiki supports Markdown and allows editing pages both through the web interface and locally via push to the wiki repository. Each Wiki page has its own change history, which is convenient for documenting API, architecture, and project processes.

The combination of GitHub Pages + Jekyll is a popular solution for documentation sites. Jekyll automatically converts Markdown files into static HTML pages, supports themes, navigation, and search. For example, the Android Developers documentation previously used Jekyll on GitHub Pages, and now uses an internal platform, but thousands of open-source projects continue to use this combination for their sites.

GitHub CLI: Management Without a Browser

GitHub CLI (gh) allows you to perform all platform operations through the command line: create repositories, manage Issues, view and approve Pull Requests, run Actions. The command gh repo create my-project --public creates a remote repository and links it to the local one, while gh pr create creates a Pull Request from the current branch. CLI speeds up work for developers who prefer the terminal over the web interface.

GitHub API for Automation

GitHub REST API and GraphQL API provide programmatic access to all platform features: creating Issues, managing users, fetching statistics, and managing Actions. GraphQL API is preferable for complex queries as it allows fetching only the needed fields in a single request. Rate limit for REST API is 5000 requests per hour for authenticated users. The API is widely used to integrate GitHub with external CI systems and internal DevOps tools.

GitHub Gist for Quick Notes

GitHub Gist is a service for publishing code snippets without creating a full repository. Gist supports syntax highlighting, embedding on external sites, and version history. Each Gist can be public (visible in search) or secret (accessible only via link). Gist is used for quickly sharing configurations, logs, and code examples in team correspondence, and also as a Pastebin alternative for developers.