List all files under a publicly-shared folder in Google Drive (in Colab), and download them

folder_list.py

from google.colab import auth
auth.authenticate_user()  # must authenticate

'''list all ids of files directly under folder folder_id'''
def folder_list(folder_id):
  from googleapiclient.discovery import build
  gdrive = build('drive', 'v3').files()
  res = gdrive.list(q="'%s' in parents" % folder_id).execute()
  return [f['id'] for f in res['files']]

'''download all files from a gdrive folder to current directory'''
def folder_download(folder_id):
  for fid in folder_list(folder_id):
    !gdown -q --id $fid

folder_recursive.py

'''This one download the folder recursively'''
def folder_download(folder_id):
  # authenticate
  from google.colab import auth
  auth.authenticate_user()
  # get folder_name
  from googleapiclient.discovery import build
  service = build('drive', 'v3')
  folder_name = service.files().get(fileId=folder_id).execute()['name']
  # import library and download
  !wget -qnc https://github.com/segnolin/google-drive-folder-downloader/raw/master/download.py
  from download import download_folder
  download_folder(service, folder_id, './', folder_name)
  return folder_name

Can test with folder_id="1HvIeNhqtFVllXFWzH5NawDdnIfgGDwCK"

What is !gdown -q --id $fid ?

It's an equivalent of

import gdown
url = 'https://drive.google.com/uc?id=' + fid
gdown.download(url, None, True)

how to use this function? Can you please explain step by step?
I am new with colab.