(Note: This is to set up your individual blog, not to post a blog)
First make sure you're logged in. You should see "Welcome, {your user name}" in the right corner.
Click on the "My Active" link next to "Welcome, {your user name}"
You'll be on the Overview Tab of your profile and on the left there is a Popular Links menu
Scroll down to the Community section and click the "Start a Blog" link.
Go through the steps to create a blog and fill in all the required fields. (Note: your blog description has a 255 character max)
Click the "Create Blog" button at the bottom once you've completed all the steps.