To get started with Blogger, I will just refer you to the instructions I share with my students here: Creating a Blog and Writing Your First Post. (If you're curious about the overall flow, here's what the students do next after they have their blog up and running: Orientation Week.)
Multiple blogs. Blogger allows you to create 100 separate blogs, and there are no limits on the number of posts in a blog. (I have blogs with literally thousands of posts.) So, I would suggest that you actually make two blogs: one blog that will become your Class Announcements blog to share with your students, plus a personal blog that you can use as an online notebook and also as a kind of sandbox to test out different blog features that you think you might want to use in your Class Announcements blog.
Make it a habit. The best way to learn about blogging is to blog, and to blog every day. Let it become your learning diary! Did you learn something new today? Of course you did — we all learn new things every day, and a blog is a great place to keep a record of that, day by day.