If you’re building locally, it’s pretty easy to do, and is discussed in this thread
If you’re using the online IDE, click on the ‘+’ symbol that the top right to add a new file to your app. Easy as that! 
If you’re building locally, it’s pretty easy to do, and is discussed in this thread
If you’re using the online IDE, click on the ‘+’ symbol that the top right to add a new file to your app. Easy as that!