//Create folder within a folder
function example21() {
  const folder = DriveApp.getFolderById('ADD FOLDER ID HERE');
  folder.createFolder('EXAMPLE 21 FOLDER');
}

//Create file in a folder
function example22() {
  const folder = DriveApp.getFolderById('ADD FOLDER ID HERE');
  folder.createFile('EXAMPLE 22 FILE', 'This is a new file.', MimeType.PLAIN_TEXT);
}

//Create file in newly created folder
function example23() {
  const folder = DriveApp.getFolderById('ADD FOLDER ID HERE');
  const newFolder = folder.createFolder('EXAMPLE 23 SUB FOLDER');
  newFolder.createFile('EXAMPLE 23 FILE', 'This is a new file.', MimeType.PLAIN_TEXT);
}

//Get URL and name of new folder, star it, add URL in text file
function example24() {
  const folder = DriveApp.getFolderById('ADD FOLDER ID HERE');
  const newFolder = folder.createFolder('EXAMPLE 24 SUB FOLDER');
  const newFolderUrl = newFolder.getUrl();
  const newFolderName = newFolder.getName();
  newFolder.setStarred(true);
  newFolder.createFile(newFolderName,
                       "New folder URL: "+newFolderUrl,
                       MimeType.PLAIN_TEXT);
}

//Get URL and name of new folder, star it, add URL in text file (linked const & chaining)
function example24b() {
  const folder = DriveApp.getFolderById('ADD FOLDER ID HERE'),
        newFolder = folder.createFolder('EXAMPLE 24 SUB FOLDER'),
        newFolderUrl = newFolder.getUrl(),
        newFolderName = newFolder.getName();
  newFolder.setStarred(true)
           .createFile(newFolderName,
            "New folder URL: "+newFolderUrl,
             MimeType.PLAIN_TEXT);
}