Please, please, please, please, please, do not keep starting new threads on the same subjects. You had already started one on categories. I'm 10 seconds away from walking away and ignoring you.
Posts appear on the main blog page below the top navigation in reverse chronological order. What is showing up on the top navigation are static pages. You cannot put "posts" on static pages. PLEASE read the link I provided to gain an understanding of the differences between pages and posts.
You organize posts into subjects by using categories. Categories will be listed in the categories widget. The only exception to that is the iNove theme which allows you to select whether you want categories or pages to be listed in the top navigation. With the theme you are now using, there is no clean way to list categories in the top navigation.