How do I use forEach to turn an array of strings into a single string

You can't use forEach on strings. forEach is meant to be used with arrays

You can make use of join here to join an array.

let words = [
  'Loops',
  'are',
  'a',
  'great',
  'way',
  'to',
  'find',
  'elements',
  'in',
  'an',
  'array',
];

function createParagraph(words) {
  return words.join(' ');
}

console.log(createParagraph(words));