The XBox One S has virtually the same capabilities as the original XBox One, but there are some changes. The 'S' in the name stands for "Slim Version" as it's smaller & more power-efficient than it's predecessor, but there are some minor changes under the hood as well.
* One S supports up to 4K (2180p) for video & 1440p for games (after firmware update)
* Adapter is required to utilize the XBox Kinect with the S (SOLD SEPARATELY)
* Updated (2nd Generation) controllers (w/ BlueTooth support) included
As mentioned, the One S uses around 35 - 90 watts of power vs 70 - 120 watts, depending on what you're doing on the console. This may not be a major thing to consider, but it will impact your wallet (via your utility bill) in the long run.
It's pretty standard nowadays for console makers to refine their consoles & release an updated version with some improvements & refinements since the original release, even dropping some seldom-used features by players & developers as a cost-cutting deal.
Hope this sheds some light on the subject.