Introduction to
GitHub

Foundations

• What GitHub is and why it matters
• Repositories, branches, and pull requests
• Markdown for docs, READMEs, and wikis
• Code review workflows

Key facts

• Founded 2008, acquired by Microsoft in 2018 for $7.5 billion
• 100+ million developers, 420+ million repositories (2024)
• Free for public and private repos (with limits on Actions minutes)
• Available as SaaS (github.com) or self-hosted (GitHub Enterprise Server)

Anatomy of a GitHub repo

• Code tab — file browser, branch selector, commit history
• Issues tab — bug reports, feature requests, discussions
• Pull requests tab — proposed changes awaiting review
• Actions tab — CI/CD workflow runs
• Settings — branch protection, secrets, webhooks, collaborators

Essential syntax

# Heading 1
## Heading 2
### Heading 3

**bold** and *italic* and `inline code`

- bullet list
- [ ] task list (unchecked)
- [x] task list (checked)

[Link text](https://example.com)
![Alt text](image.png)

| Column A | Column B |
|----------|----------|
| cell     | cell     |

The PR workflow

Review actions

• Comment — feedback without explicit approval or rejection
• Approve — "this is good to merge"
• Request changes — "fix these issues before merging"

```suggestion
const result = items.filter(Boolean);
```

Issues

• Title, description (Markdown), labels, assignees, milestone
• Templates: .github/ISSUE_TEMPLATE/bug_report.md or YAML forms
• Close issues automatically: Fixes #42 in the PR description
• Pin up to 3 issues to the top of the Issues tab
• Transfer issues between repos in the same org

Complete workflow example

# .github/workflows/ci.yml
name: CI
on:
  push:
    branches: [main]
  pull_request:
permissions:
  contents: read
jobs:
  lint-and-test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [18, 20, 22]
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node-version }}
          cache: 'npm'
      - run: npm ci
      - run: npm run lint
      - run: npm test -- --coverage
  build:
    needs: lint-and-test
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm ci && npm run build
      - uses: actions/upload-artifact@v4
        with:
          name: dist
          path: dist/

Reusable workflows

Define a workflow in one repo, call it from others. DRY for organisation-wide CI standards.

jobs:
  deploy:
    uses: my-org/shared/.github/
      workflows/deploy.yml@main
    with:
      environment: production
    secrets: inherit

- uses: actions/cache@v4
  with:
    path: ~/.npm
    key: npm-${{ hashFiles(
      '**/package-lock.json') }}
    restore-keys: npm-

Installation

# macOS
brew install gh

# Ubuntu / Debian
sudo apt install gh

# Windows
winget install GitHub.cli

gh auth login
gh auth status
gh auth switch

gh pr create --title "Add X" \
  --body "Description"
gh pr list --state open
gh pr checkout 42
gh pr review 42 --approve
gh pr merge 42 --squash \
  --delete-branch
gh pr checks 42

Issue operations

gh issue create \
  --title "Bug" --label bug
gh issue list --assignee @me
gh issue close 99

Actions from the terminal

gh run list
gh run view 123456
gh run watch 123456
gh run rerun 123456
gh workflow list
gh workflow run deploy.yml
gh workflow run deploy.yml \
  -f env=staging

# Get repo info
gh api repos/owner/repo

# List PR comments
gh api repos/owner/repo/\
  pulls/42/comments

# Create a label
gh api repos/owner/repo/labels \
  -f name="priority:critical" \
  -f color="d73a4a"

GitHub Pages

Free static site hosting directly from a repository.

• Serve from main, gh-pages, or /docs
• Custom domains with HTTPS (free Let's Encrypt cert)
• Built-in Jekyll support, or any static site via Actions
• URL: username.github.io/repo-name

# .github/workflows/pages.yml
name: Deploy to Pages
on:
  push:
    branches: [main]
permissions:
  pages: write
  id-token: write
jobs:
  deploy:
    environment:
      name: github-pages
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/upload-pages-
          artifact@v3
        with:
          path: './dist'
      - uses: actions/deploy-
          pages@v4

Dependabot

• Alerts — notifies when dependencies have known CVEs
• Security updates — auto-opens PRs to bump vulnerable deps
• Version updates — keeps dependencies fresh on a schedule

# .github/dependabot.yml
version: 2
updates:
  - package-ecosystem: "npm"
    directory: "/"
    schedule:
      interval: "weekly"

Single application philosophy

• Built-in CI/CD — .gitlab-ci.yml, no marketplace
• Built-in container registry — every project gets one
• Built-in package registry — npm, Maven, PyPI, NuGet
• Built-in wiki — per-project, Git-backed
• Built-in SAST/DAST/SCA — security scanning in the pipeline
• Review apps — deploy a live preview for every merge request

Example pipeline

# .gitlab-ci.yml
stages:
  - build
  - test
  - deploy

build:
  stage: build
  image: node:22-alpine
  script:
    - npm ci
    - npm run build
  artifacts:
    paths:
      - dist/

test:
  stage: test
  image: node:22-alpine
  script:
    - npm ci
    - npm test -- --coverage

deploy_production:
  stage: deploy
  environment:
    name: production
  script:
    - ./deploy.sh production
  when: manual
  only:
    - tags

When to choose GitHub

• Open-source — largest community, discoverability, contributors
• Teams already using the GitHub ecosystem
• Projects that benefit from the Marketplace
• When Copilot and AI-assisted development are priorities

Bitbucket (Atlassian)

• Tight integration with Jira and Confluence
• Bitbucket Pipelines for CI/CD
• Free for up to 5 users on private repos
• Best for teams in the Atlassian ecosystem

What we covered

• GitHub as a platform — repos, branches, PRs, and code review
• Markdown on GitHub — GFM, extensions, where it's used
• Issues and Projects — lightweight project management
• GitHub Actions — workflows, syntax, advanced patterns
• GitHub CLI — terminal-driven workflows with gh
• Pages, Releases, and Packages — hosting and distribution
• Security — Dependabot, CodeQL, secret scanning
• Copilot — AI-assisted development
• GitLab — platform overview, CI/CD, unique features
• GitHub vs GitLab — when to choose each