You need to install and activate Webnus Portfolio from here: Install Plugins. Then a new menu will be added to WordPress dashboard panel called Portfolio.
Portfolio: shows all the posts.
Add Portfolio Item: you can add a new post.
Portfolio Category: you can set categories.
Webnus Portfolio Options
In Portfolio Options, you can set which style to be shown for the next and previous post navigation links. You can also show the Related Works, you need to check its checkbox.