On our first day of class, we got acquainted with the course goals and a little with the technological tools we'll be using this semester, one of which is a blog.
To learn to write well takes a lot of practice writing. So, one purpose of the blog is to let you write a lot on a topic you're interested in. Writing well also requires a lot of reading. While writing on the topic you like, you'll need to do some research, find out others who are writing on your topic, read their blogs, respond to their writings, and learn more about the topic.
Because we will subscribe to each other's blogs, we'll learn more about writing because we'll see what others do when they write, and so on.
Of course, we'll still write academic essays, four of them. Academic essays will focus more on academic writing, while blog writing will help you make your writing skills more automatic, letting you think more about your ideas and your organization when writing the academic essays. Each type of writing will re-inforce the other type, and so you should see your writing improve a lot over the semester.