Create your portfolio post in Portfolio>Add new. Type title for it, assign to existing category or create a new one and upload featured image to it.
To add some text to your portfolio post, go to Portfolio content section and switch to Item additional info tab. Type text in Portfolio description field. This will be the main portion of text on page. You can also add additional information, that will be displayed like bulleted list without bullets. In front of the Additional info title, enter title (optional). And in front of Additional info click on Add new button and fill in Title and Description fields.
There are additional options to show/hide social share button, enable/disable related portfolio items and choose number of related portfolio items.
After you have added content, your portfolio item will look like that.
The above layout of portfolio is not the only one available and you can change it to another one. In Portfolio content section switch to Item layout options and change layout to any other represented by the image thumbnails.
You can also show other media instead of featured image, such as image gallery, video or audio file. For this choose corresponding thumbnail in Portfolio content>Item layout options>Item media options. After you have chosen any of the thumbnails, there appears a metabox field where you should add image gallery/video file/audio file. 
There is option to display portfolio items in a masonry layout with different sizes of featured images. If you would like to have such a masonry page, choose size for portfolio featured images in Portfolio masonry section in the upper right corner of the edit page.

There are additional options to adjust portfolio page appearance. Scroll down the edit page and in Page options section you will find options to adjust the following: color scheme, top panel, header options, stunning header options (page title section), footer options and page layout. 