You can do this by going to the "Posts and Comments" area of your Blog Module.

YourDomain.com > Modules > Blog: Blog (mX) > Posts & Comments

Clicking on "Add Post" will take you to an editor where you can create a new post

NOTE: once you save your new post it will be visible (live) on your site

Here is what the create a post page will look like:

You can choose the Author.  (note the author is anyone that is setup in the membership module linked to this blog module, and specified in the "General settings" area)

The "Name" is the title of your blog post.

Categories will decide who gets the notification about this post, and where it is stored.

You can also post your blog to your facebook wall, if you have it setup do to so in the "social media integration" area.

Clicking on "Add" will post your new Blog post.

If you have any questions please feel free to contact support.