question: Please write a detailed guide on how to set up a new Jekyll blog on GitHub Pages. Make sure the guide is in English and all section headings are in capital letters. At the end, include a postscript explaining how to troubleshoot a common issue with deploying Jekyll sites on GitHub Pages.
answer: # INTRODUCTION
  
  Jekyll is a static site generator that is perfect for creating personal blogs or project pages. GitHub Pages provides a simple way to host these static websites for free. This guide will walk you through the process of setting up a new Jekyll blog on GitHub Pages.
  
  # PREREQUISITES
  
  Before you begin, ensure you have the following:
  
  1. A GitHub account
  2. Ruby installed on your local machine
  3. Bundler and Jekyll gems installed
  
  # SETTING UP YOUR LOCAL ENVIRONMENT
  
  1. **INSTALL RUBY**: Make sure Ruby is installed. For macOS, use Homebrew:  
     ```bash
     brew install ruby
     ```
  
  2. **INSTALL BUNDLER AND JEKYLL**: Use the following command to install Bundler and Jekyll:  
     ```bash
     gem install bundler jekyll
     ```
  
  # CREATE A NEW JEKYLL SITE
  
  1. **CREATE A NEW DIRECTORY**: Navigate to the directory where you want to create your blog and run:  
     ```bash
     jekyll new my-blog
     ```
  
  2. **NAVIGATE TO YOUR SITE'S DIRECTORY**:  
     ```bash
     cd my-blog
     ```
  
  3. **INSTALL DEPENDENCIES**:  
     ```bash
     bundle install
     ```
  
  # TEST YOUR SITE LOCALLY
  
  1. **BUILD YOUR SITE**:  
     ```bash
     bundle exec jekyll serve
     ```
  
  2. **VIEW YOUR SITE**: Open a web browser and go to `http://localhost:4000` to see your site.
  
  # SET UP GITHUB PAGES
  
  1. **CREATE A NEW REPOSITORY**: Go to GitHub and create a new repository named `yourusername.github.io`, replacing "yourusername" with your GitHub username.
  
  2. **INITIALIZE GIT IN YOUR PROJECT DIRECTORY**:  
     ```bash
     git init
     ```
  
  3. **ADD REMOTE ORIGIN**:  
     ```bash
     git remote add origin https://github.com/yourusername/yourusername.github.io.git
     ```
  
  4. **COMMIT YOUR SITE**:  
     ```bash
     git add .
     git commit -m "Initial commit"
     ```
  
  5. **PUSH TO GITHUB**:  
     ```bash
     git push -u origin main
     ```
  
  # CONFIGURE YOUR REPOSITORY FOR GITHUB PAGES
  
  1. **GO TO YOUR REPOSITORY SETTINGS**: On GitHub, navigate to the "Settings" tab of your repository.
  
  2. **ENABLE GITHUB PAGES**: Scroll down to the "Pages" section. Choose the branch you want to use (usually `main`) as the source and save.
  
  3. **ACCESS YOUR BLOG**: After a few minutes, your site should be available at `https://yourusername.github.io`.
  
  # CUSTOMIZE YOUR BLOG
  
  1. **EDIT CONFIGURATION FILE**: Open `_config.yml` in your project directory to change the title, author, email, and other settings.
  
  2. **ADD CONTENT**: Create new posts in the `_posts` directory. Posts should be named with the format `YYYY-MM-DD-title.md`.
  
  # POSTSCRIPT: TROUBLESHOOTING COMMON ISSUES
  
  A common issue when deploying Jekyll sites on GitHub Pages is the "Page build failed" error. This often happens due to incorrect gem dependencies. A quick fix is to ensure you're using the `github-pages` gem, which matches the environment on GitHub Pages. Update your `Gemfile` to use:
  
  ```ruby
  gem "github-pages", group: :jekyll_plugins
  ```
  
  Then run:
  
  ```bash
  bundle update
  ```
  
  This aligns your local development environment with GitHub's build environment, reducing the risk of deployment errors.