its an app on your phone that allows you do some cool remote things, like lock/unlock, remote start (with climate controls), you can set alerts, schedule appointments and view recalls/car issues. I have not had a practical use for it but the few times I have used it, it was slow to remote start. I think the issue that most people have is a tad slow and, after your free year is up, its quite pricey for the top tier plan that allows for remote start. 2021 owners wont have to worry as they will get fob remote start standard and there are a few aftermarket fob remote start options for about 299, which is about what UVO costs once you are done with your free year.
Here is a snap of what you get for free, for year 1. Its about 30/mo after that.