Why users never (or almost never) read the doc?
In the FAQ, it’s written:
What about the Portfolio Category Shortcode?
A shortcode is included into the plugin to display the projects belonging to a particular category into a page. Usage: [birdsfolio cat=”slug_of_the_portfolio_category_you_want_to_display”] slug_of_the_portfolio_category_you_want_to_display must be unique and it must be the slug of the category.
There will be no filtering, of course, but projects will use the masonry display.
In the Installation tab, it’s written:
4. Visit Settings > Permalinks in your WordPress admin to flush your rewrite rules.
5. Create a page and select the ‘Portfolio’ template in the Page Attributes block.
What is confusing?
If you have different categories, then you can create a page, choose the portfolio template, and that’s it.
When this page is displayed, the portfolio is displayed, with filtering.
If you want to display only one category on a page, then you can place a shortcode in the content of this page.