GitHub Actions are a suite of user and GitHub created abilities which allow you to declare a pipeline straight in GitHub. They permit your project to build and deploy different components without the need for spinning up your own CI/CD infrastructure. GitHub Actions run using docker containers which allow you to bake in any required dependencies.

A bundle of actions is called a workflow on GitHub and it exists within your repo under .github/workflows/, if you do not have the folder you can create it using mkdir -P .github/workflows in top level directory of the repository.

name: github pages
      - develop

    runs-on: ubuntu-18.04
      - uses: actions/checkout@v2
          submodules: true
          fetch-depth: 0

      - name: Setup Hugo
        uses: peaceiris/actions-hugo@v2
          hugo-version: 'latest'
          extended: true

      - name: Build
        run: hugo --minify

      - name: CNAME
        run: |
          echo "" > ./public/CNAME

      - name: Deploy
        uses: crazy-max/ghaction-github-pages@v1
          target_branch: master
          build_dir: ./public
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}      

Above is an example workflow which utilises the GitHub Action checkout to checkout the code, Actions Hugo by Peaceiris to provide the necessary prerequisites to build the Hugo website and ghaction github pages by Crazy-Max to push the contents of the public folder, where the static files are created after running hugo --minify to the master branch, where GitHub pages is expecting the website to be.

This workflow is kicked off when there is a push to the develop branch, this results in a fresh website build after pull request are merged to develop. You can see how this website and the workflow work by going here