Provided you’re talking about something that you’ve written or have permission from the copyright holder to post, you upload it as a Post and then add categories to it. Categories are not a “section.” They are a way of organizing your posts.
You may be getting confused between Link categories and Post categories. Here:
Uh, you don’t upload a link. You write some text, perhaps with a block quote, and then link to the source. You cannot post entire articles from elsewhere on the web to your blog unless you wrote them yourself or got specific written permission from the author. It’s illegal.