title: after downloading express-generator, express still cannot be used
body: <p>I am working on a small project. However after I download express-generator ( npm install -g express-generator) still couldn't use express. Really don't now why. Anyone can help? Thank you so much! Please see the screen shot below:
  <a href="https://i.stack.imgur.com/YbByf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YbByf.png" alt="enter image description here"></a></p>