Fortnite Battle Royale is yet to be released on either Android or iOS. It's currently in an invite-only pilot mode, where the developer, Epic Games is controls who can play it to fine tune and test the game play, backend, and controls before launching it fully. The first set of people who got invites also got few additions to bring along their friends: those are the only few who can currently play the game on mobile. More invites will be out soon. Eventually, everyone will be able to play as they wish.
Currently, the pilot program is available only on iOS, and in fact on specific devices. You can play the Fortnite game if you've got at least an iPad Air 2, iPad Pro, iPad Mini 4, iPhone 6S/SE, or 2017 iPad devices. The game is quite intense for a phone to run, so do not expect a change in requirements. Also, you should get an external battery pack, as the Fortnite Battle Royale will kill your battery.
Currently, Bluetooth controllers aren't enabled for the Fortnite Battle Royale game on mobile, but the developer is making plans to eventually bring them. This implies that everything is currently done through touch controls, which isn't as cool as a keyboard and mouse or a controller. Your character is moved with a virtual joystick located in the lower left, and you drag the screen with your right hand to look around. To open doors, you can either run into them or tap them – weapons will be picked up automatically if you do not have enough room for them, and tapping them directly will swap out your current equipped weapon. The virtual on-screen buttons are used for every other action, from aiming, to crouching and shooting.
It may not be perfect, but it definitely works. Besides, every of your opponents will also be using the same controls.
In Fortnite Battle Royale, no matter what platforms are being used, any 2 players can easily play together, unless the 2 platforms are PlayStation 4 and Xbox One. All other pairings are fair games – this implies that the game can be played on mobile. In Fortnite, Cross-play is a social feature, and it is opt-in – which means that players on mobile can only play with other players on mobile unless they squad up with a player on a PC or console.