See the guide at https://wpportfolio.net/docs/getting-started-with-wp-portfolio/
When you select a portfolio type, you are selecting a type for the individual portfolio item you are adding.
Basic overview
Website
Not just for websites – this is the type for an image that links to a URL (e.g. shop items on another site).
Each entry has a Thumbnail image and a URL can be set to be used when a visitor clicks on it.
Image
Basically a simple Image Gallery. Images can be showcased with filters.
Each entry has a thumbnail image and a portfolio that will be shown when it is clicked.
Video
A video gallery with sorting and searching options.
Each entry has a thumbnail image. Clicking on it will open a video in the iFrame.
Single Page
You create a single page for each entry and showcase them with filterable tabs.
Each single page can be designed with WordPress default editor or with any page builder.
Each entry has a thumbnail image and clicking on it will open the full page.