(Taken from Wikipedia)
Virtual reality (VR) typically refers to computer technologies that use software to generate realistic images, sounds and other sensations that replicate a real environment (or create an imaginary setting), and simulate a user's physical presence in this environment, by enabling the user to interact with this space and any objects depicted therein using specialized display screens or projectors and other devices.
To be able to use VR, you need VR hardware and a compatible smartphone. As for whether your HTC device is VR-ready, I'm unsure, but you can check the following website to see if your phone model is compatible:
https://www.freeflyvr.com/top-10-htc-smartphones-ready-for-virtual-reality/