Unreal engine is freely available via the Unreal website or the Epic Games Launcher.

A list of system requirements can be found here:

https://dev.epicgames.com/documentation/en-us/unreal-engine/hardware-and-software-specifications-for-unreal-engine

Unreal Engine can be system demanding so keep that in mind. Unreal engine works on Windows and Mac systems and allows for deployment to Android, iOS, Console, PC, VR and beyond however these may require additional software and licenses for example is wanting to create an iOS application you will need Xcode, an Apple developer license and Mac hardware.