What exactly am I buying into if I buy something like UVXY?

As I understand it it’s tracking VIX futures, and I understand at least at a basic level what VIX is. But like, what exactly am I buying if I open my brokerage and buy 1 share of UVXY?

For example, if I buy a share of APPL I am buying a small stake in Apple, if I buy something like SPY I am buying into a pool of companies. But, what am I buying if I purchase shares of UVXY?

I don’t want to actually load up on shares of them, but I’m just curious what it even is and why it’s a thing you can spend money on if it’s not like a company or some real thing with value? Or am I stupid and it is something like that?