Samsung patent details how the foldable Galaxy X may operate

In terms of how Samsung envisions the smartphone, it appears the South Korean company will be treating the two portions of the display as separate panels. Thus, when the smartphone is folded slightly, the bottom portion, which makes up 60% of the total, will be deactivated, leaving just the upper half in operation. This is achieved via a built-in sensor that detects not only when the smartphone is bent, but also the angle and speed at which this has been done, and how long the position has been maintained for. Also, it’s understood that a separate sensor will be able to detect to what extent the user is gripping the rear of the smartphone – when the user is not touching the rear, the display will be able to return to its unbent state automatically. 

Functionality wise, the patents reveal that the top portion of the display will be used primarily to display relevant information to the user whenever the device isn’t in use, although if owners wish to interact, a small amount of pressure on the rear will activate the touch capabilities. Also, if this pressure is maintained, the bottom half of the display will be activated, although it will continue to operate as a separate display. Nevertheless, just like any traditional smartphone, those who purchase the foldable Galaxy X will also be able to use the display as one large panel whenever the device is completely unbent.

Considering this is simply a patent, there's no guarantee the Galaxy X will function as described in the filing. However, with the release currently set for January at CES 2019, the brand's most recent patents most likely provide some kind of hint at how the Android device will work.

source: LetsGoDigital (translated)