How to configure the Portfolio

First you need to make sure that it's enabled from Appearance > Customize > Portfolio section. If it is, then you need to navigate back to your Dashboard and add some items into your Portfolio. The option to add items to your Portfolio is available in your Dashboard menu. There should be, at least, one portfolio item, in order for the Portfolio section to show up.

And make sure that you've added a Featured Image to your Portfolio item. If there isn't a Featured Image then it won't appear on the front page.