What is the Post Status?

One of the blue boxes on the right when you compose a post is called “Publish Status“

“Unpublished” is the default. When this is selected clicking “Save” will save the post as a Draft. It will then appear at the top of the Write Post page and Manage Post pages as a Draft until it’s status is
changed (such as publishing it). Clicking “Publish” will publish a Draft to the blog.

“Published” Selecting this will publish a post when you click either “Save” or “Publish”.

“Private” Selecting this option will make a post private. This means that the post will be visible on your blog, but only to you when you are logged in. A post marked Private will be listed alongside published posts on the Manage Post page. Posts which are Saved as Private are not visible to Blog Surfer. They are completely invisible to everyone except you (and will be invisible to you if you are not logged into wordpress.com).
They are also invisible to your blog’s Search widget.

You may change the status of a previously published post by editing it and changing it’s Post Status to either “Draft” or “Private” and clicking “Save”. Changing a post’s status to Draft means it will be listed as a Draft on the Write Post and Manage Post pages. All comments will be preserved. Likewise, if the status of a previously published post is changed to Private then Saved, the post’s comments  will be preserved and the post will be visible only to you (see above).

A published post is also then available in your blog feed. If you change the post to Draft or Private you cannot stop the already posted information for people reading your feed.