There are different ways of posting in Blogs and making these posts visible within Moodle.
1. The easiest way is to post directly into the internal Moodle blog page. Click on "Add a new entry" in the Blog Menu block and insert your message.
2. Use your own private Blog page to insert your message and link the RSS feed of your blog page to the course (click on Preferences/Blog under your photo at top of page. Then click on Preferences in Breadcrumbs thread and External Blogs/Register an external blog, under Blogs, to syncronise and verify your Blog RSS).