Samsung DeX essentially allows you to continue work from compatible apps on your Galaxy S8 from a traditional computer setting. To get it to work, you'll need the DeX dock (sold separately), a monitor, keyboard, and mouse. Given that DeX is powered by the Galaxy S8, which runs on Android, it's important to know that it cannot run Windows or Mac OS apps and programs, and likely isn't a complete desktop replacement for most people. Still, it seems like a decent option for people who conduct work on both their smartphones and computer.
While operation is much like you'd expect from a traditional computer, DeX is essentially giving you a larger space with more tools from your Galaxy S8, which, despite its larger display, can still be too small to effectively work on some projects.
Samsung isn't the first to employ this idea, as devices like the HP Elite x3 and Motorola Atrix/Photon have attempted this in the past, but with little fanfare. Microsoft also has Continuum for its Lumia 950 and 950XL devices. Will Samsung's solution, which is arguably equally as limited, be any better? It's possible, but only time will tell.
Pricing and availability isn't official yet, but it's been leaked that the DeX dock will sell for around $160 US.