If what you want is a web app then I would look for the first-in-class tutorials for a given framework/language. This assumes you are comfortable with a given language.

For Rails that would probably be https://www.railstutorial.org/.

For Meteor, that would be https://www.discovermeteor.com/.

I can't speak to Django or Flask. Or node based platforms like Sails.

I would recommend the Rails tutorial even if you don't ultimately settle on Rails. There's something magical about that tutorial. I recommend it now even though it is not my platform of choice.