Magento 2 app/code and app/design difference

Question

I'm curious what should be the proper way of using these two folders. Normally when I create my own module. I include everything (php, phtml, css, js, images) under my app/code module. Which somehow works and easy to navigate into.

But I have a feeling I'm misusing this. Can someone enlighten me? Can't find anything from the documentation discussing how this two directories should be treated.

Thanks!

Answer 1

The main different of app/code and app/design is the when we developed our own module which can define in app/code and when we developed our own theme we can use the app/design that is the main different between this two.

simple thing is for custom module development use app/code and custom theme creation use app/design.