Creating the Portfolio Page:
1. Go to the section that says ‘Portfolio Items’ and create a parent category e.g. Portfolio. Ensure that the slug (which will be the url) says something slightly different, like ‘portfolio_cat’.
2. Create sub categories, e.g Photography, Design, Illustration and assign those to the ‘Parent’ category ‘Portfolio’.
3. Go to Pages, and create a new page and call it ‘Portfolio’. Also, make sure the ‘Permalink’ at the top of your new page is slightly different, e.g. ‘portfolio_page’.
4. Go to back to the ‘Portfolio Items’ section in the side bar, and click on ‘Add New’.
5. On your new item page, add some descriptive text in the text field about your project. Then ensure (and this is VERY, VERY important) you add a ‘featured image’ (this is the one that will be included on your ‘Portfolio’ page). Then add ‘exta images, with caption and descripion. Save.
6. In the ‘Appearance’ section, go to Menus. If you have not already done so, then create your Menu and add your pages. Add your Portfolio page from the ‘Pages’ box. It will appear at the bottom of the list on the right, drag it to where you wish it to appear in your menu. Then go to the ‘Items’ box, click on each item you want to be in the menu. Then drag them up to the Portfolio box, though move the item boxes slightly to the right, so they will appear as sub menus on your site. Then save the menu.
7. Open your Portfolio page and use the Portfolio shortcode generator (which is a little icon). You must make sure that in the section that says ‘Category to show’ you have chosen the parent category, e.g ‘Portfolio’, then choose how many colomuns you wish etc and click on submit. That should do it. Make sure that in the shortcode on your page you see the correct ‘cat id’ for the parent category. You can check it is the correct id by going to ‘Portfolio Categories’, hover over the parent category and the url for that category will appear at the bottom of your browser, so you can check that the id is the same.
8. Save page, cross fingers for luck.
ps: only one remark from the author: you don’t have to use portfolio custom post type (and categories). You can use and normal blog posts and categories. There will be no difference on portfolio page, only single posts will have different layout.