Can I use Apple Watch 4 without owning an iPhone?

The watch is not really a standalone device, really the only way the watch can be used is with an iPhone also. the watch is not compatible with any other operating system such as Android. There are other smart watches that will work with iPhone and Android but most of them run some flavor of the android software so even those devices will work better on droid than they will on iPhone.

You can own it, but you will not be able to setup or use the watch without an iPhone.