The difference between HDR and standard coloration in an image or video can be quite literally night and day, as seen in the attached screenshot from a Netflix original show based on Marvel's Daredevil property. Everything is more crisp and real, blacks are deeper, and bright colors pop far more. The naked eye can tell the difference easily, but for those interested in the facts, HDR post-processing, on average, allows anywhere between 600% and 800% more color to come through by pushing out a wider gamut of colors. HDR has to be used with care, of course - it's easy for colors to become washed out, or for a blaring pair of headlights or bright overhead light to blind the viewer to the rest of the scene. These are all things that Netflix has to take into consideration as they get ready to flip the switch on HDR content.
HDR content for Netflix will happen on their side, and will be compatible with any HDR display out there, including supporting phones and tablets. A good number of high-end TVs out there, along with the likes of gaming laptops, high-end PC monitors, and of course some mobile devices, all support HDR out of the box. Still, HDR compatible displays are a fairly new innovation in the land of display technology, so not all customers will have what's necessary to see the new content. For those that do, no extra legwork, hardware, or software will be required.
The way Netflix is going to implement it is by offering two different versions of their content, for now; when the service detects an HDR-compatible device or display, it will output the right content, if it's present for that particular show. Otherwise, the standard SDR content will be shown. HDR content won't require much from the customers, but Netflix will have to have their staff put in extra hours adjusting color values to get the HDR coloration right, and then having color critics look over the program to ensure that viewers are getting the optimal experience. For now, Netflix has not laid out a timeline for when viewers can expect to start seeing HDR content.