You don't need those pages. You need only the link to the Category. Like, on my blog I have the category Cthulhu. The category link is http://raincoaster.com/category/cthulhu and if I wanted to do what you're doing I'd put THAT link in. You don't need static pages at all.

Step 1. I created another page that isn't the Home page called Fashion

Step 2. I created a sub page called trends

Step 3. Created a custom menu with page fashion + page style

Step 4. Added my existing category called fashion to the menu.

Step 5. Saved created menu.

But I still have a blank page when i click on my Fashion page and my style page (no posts from the category fashion).

Where did I miss a step?

Pages and posts are entirely different things: http://en.support.wordpress.com/post-vs-page/

Now, if you want to have a fashion page, what you do is use the tag or category Fashion on those posts. Then you use a custom menu to link to that category page in the header http://en.support.wordpress.com/menus/