Migrating Joomla K2 nested categories I have a large-ish site built with Joomla and K2, with articles stored in a hierarchy of categories..

What is the proposed way to recreate the Category hierarchy functionality?

What I am interested in is that when a user opens a parent category, he sees all items stored in this category, plus all items stored in children categories.
If he opens a child category, he sees items stored only in this category.

I have tried a demo installation, and experimented a bit with section types and categories, but what I need is some kind of parent-child relation in Categories or Sections. 

Could you please help me clarify how these things are distinct and what would be best practice to achieve what I want?

Thanks in advance for your time.
Craft supports hierarchical, nested categories out of the box.

It also supports hierarchical entries, assuming you used the Structure section type (and not a channel or single).

Where Craft and Joomla differ is the output on the front end is completely up to you. There's no default "widget" or anything in Craft that is going to do exactly what you want.

Craft's {% nav %} tag would help you output categories and sub categories. This example uses a structure section but it's also applicable to nested categories as well.

There's a few recipes in the Craft Cookbook that you might find helpful in this instance as well.