Using action to deploy to staging/preview url and working directory should be build or root dir

[Pranav016]

name: deploy website
on: [pull_request]
jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      #  your build commands
      # - run: |
      #    ng build --prod
      - uses: amondnet/vercel-action@v20 #deploy
        with:
          vercel-token: ${{ secrets.VERCEL_TOKEN }} # Required
          github-token: ${{ secrets.GITHUB_TOKEN }} #Optional 
          vercel-args: '--prod' #Optional
          vercel-org-id: ${{ secrets.ORG_ID}}  #Required
          vercel-project-id: ${{ secrets.PROJECT_ID}} #Required 
          working-directory: ./sub-directory

If I remove the vercel-args: --prod input from the action then would it deploy to staging? Because that's what happens when we run vercel command locally without the --prod flag.
I want to deploy my PRs to staging/ a preview url before merging which I'll deploy to production.

Also, I am working on a react app thus the working-directory input will be my build folder(./build) right ? That I want to deploy or will it be the root dir of my project?