The Samsung Gear VR has gone through several iterations. This is the latest and it is compatible with Samsung PhoneCast. If you use it with a Galaxy 8 or 9 you can download the PhoneCast app and use most of your phone apps through the headset. (However, note that if you have the Galaxy 8, you must get the particular version of the headset designed for that model, because of size differences).
The Gear VR is built for use with Oculus software, so you need the Oculus app download and account to get the games that will run on it.
Bear in mind that Gear VR is something of a bridge between the low-end phone housing VR headsets and the high-end proprietary VR headsets: Oculus Rift, HTC Vive and Sony PlayStation VR. The Gear VR is unique in having features of both. It is based on the phone housing concept, but it runs Oculus games. Unlike the big boys, it is untethered and a true standalone. It needs no expensive and bulky computer hardware to run. It also neither has nor needs any lighthouses or towers to track its position.
This has several downsides. For a start, the image quality is limited by the resolution of the phone. Secondly, the head tracking is limited to 3 degrees of freedom, rather than the 6 of the Rift and Vive. This means that while it can follow your head as it turns, leans or moves forward and back, it cannot track as you move forward and backward, left and right or up and down.
There may also be a problem of latency, depending on how good the phone is - and how much "stuff" it has running in the background.
On the other hand, it has the benefit of giving you access not only to Oculus games but also the ability to use Android apps in a virtual reality environment. It also comes with a small and handy remote control that is good enough for most games - although some Oculus games require a bluetooth gamepad, which is one point on the downside, but hardly a deal breaker.
Depending on the resolution of the phone screen, you may find that individual pixels are sometimes visible. But the visual quality, was on the whole very good for a headset in this price range. Also, it is light and very comfortable to wear.
The unit has a USB C-type port at the bottom, so it is possible to charge the phone without removing it from the headset.