Composer (Ctrl + I) is the feature to use for multi-file creation and editing.
Here is a simple example of how it can be used:
Note, the screenshots in that post are from a few versions ago, so it looks a bit different, but the main functionality is essentially the same - eg, tell it to create a simple html site with js and css that tells funny pirate jokes and has a color scheme inspired by the timber in wooden ships, and it will generate all the files for you .