An Aside is a special Post Type that will appear in the news content stream like an ordinary blog post … but without the title, but not in all themes. If not you can design your own aside. Handy if you want your blog to look more like social media stream without the annoying adverts …
Category: First things first
This is the default category for posts. If you forget to create a category it will go here. If you delete a category, the associated posts will end up here. If you cannot be bothered with categories, you can hid the category in many themes.