Go to the Portfolio menu. Click on the Add item button at the top.
Set the title then you can create your content in the editor via the default WordPress editor or by switch to the Visual Composer Backend or Frontend Editor. On the right you can set filters. Later on you can filter your portfolio by that. Below the filters set your Featured Image. Portfolio is sorted by date, so you can modify the order by changing the published dates. Finally click on Publish.
You can simply add a portfolio section to your page by using the Portfolio Visual Composer element.