The title says it all. I see many poasts either in blogs or other groops were people just pasted audio files as recordings and i have no idea how that works

In the blog post creation window, there should be an option for audio content, and then, you just select "use existing file", just like in the forum.

Or you can just record one there

If you change your input to VAC, VB cable or anything that's capable of routing system audio, you can record one using that method.

Easier way is select recording from disc in audio post creator.