Until now, people have been writing ‘comments’ rather than ‘posts’. I can see why: it’s a little easier (but only a little easier). The intention is that when you want to write something, you create a post, and then make sure to choose the correct category in the list of categories at the right. So this post is an example of that.
A benefit of writing posts is that other people can comment specifically on your post. That way it’s easier to get a dialog going.
Jack