If you are reading this, congratulations! You found it, you got this far. If you want to read and comment on your classmate's posts, you can do it from here, much like you would any other blog.
BUT, if you want to make your own post, you will need to open up another page. Go to http://blog.lib.umn.edu/uthink/ and on the righthand side click "Login to UThink." On your dashboard, under "My Blogs" you should see "Intro to Sociology." Once you click it, you select "Entry" from the "Create" pulldown menu. Make sure you add tags and a category once you've written your post so it will be easier to find.