If you have already made a new blog, but you can’t figure out how to post, here is the likely issue: you’re trying to post to the blog Scott maintains, the course blog, the general and mostly official Feeling Networked blog. You need to post to your own personal blog. To switch to that blog, you need to click on the “My Sites” at the top left (to the right of the WordPress logo), and select the blog you have set up.* Once you are there, you can create a new post either by clicking selecting “Post” from the “+ New” menu up top, or select Posts from the dashboard menu on the left.
*The class blog is also one of “your sites,” although you are signed up as subscribers, and can only comment.
Here’s a handy screenshot that may help: