In order to create a navigation bar, choose "layout" on the dashboard screen. There is a "Navbar" section on the screen. But it is useless for navigation within a blog, so ignore this.
Choose "Add a Gadget" under the Header section.
Scroll down the list of gadget to find "labels" to add.
Then this pop up window will show.

Remove the title name to leave it blank.
Select "selected labels". Use "edit' to choose the labels you need for navigation bar.
For sorting the labels, use "Alphabetically", therefore when you decide what label name to use for each  groups, choose wisely so that your labels could be grouped in alphabetical order and still can be presented in a way you desire.
Untick "Show number of posts per label". Then save.

Whenever there is a new article to post, choose to group it under which tab by using the exact label for the article.
For adding new tabs on the navbar, add new labels and repeat the three steps describe above.

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