Categories or portfolios? I'm confused

I’m using the page builder and when working on certain ‘boxes’ it sometimes asks for certain categories whilst other times I see similar ‘boxes’ asking for portfolios’

what the hell is the difference?

I’ve found a number of tutorials but they seem to address this in different ways (some with portfolios and others with categories) so I figure i’d do much better if I was to understand what each one is for and then I could work out which tutorial I need to follow.

Before you ask, yes it’s a premium theme and no it’s not worth sending my technical support to Ozythemes because they don’t respond to technical support from customers (i wish i never purchased from Ozythemes – they suck)