The hype for Fortnite on Android has taken the web by storm, but those who want to jump into the action a little early can do so via Steam Link, if they have a compatible PC, a controller and a decent connection. There are a few caveats to this method, of course; first off, you'll need a Windows PC or Mac with Steam, and you'll need to link Fortnite to your Steam client by adding it as a non-Steam game, since Epic did not put it on Steam. The biggest catch is that this method only works when your phone and computer are on the same Wi-Fi network.
First, grab the Steam Link app from the Play Store if you don't already have it. From there, hop on the same network as your gaming PC, then fire up the app. It should detect your PC, and you'll have to enter a PIN on the host machine to get things rolling. From there, grab your Bluetooth controller, or a USB controller and USB on-the-go adapter, and open up your machine in the app. It will log into your Steam account through the computer and open it up in Big Picture mode. Almost all compatible Bluetooth controllers will need no setup; Steam Link will use Steam's built-in control remapping to automatically make your computer treat them as Xbox 360 controllers. So long as your connection and your computer are fast enough, you're now free to play Fortnite while soaking in a bath, sitting on the porch, at the table, or anywhere else in or around your home where you may not want to lug your computer.
Though the setup for Steam Link is fast and easy, the big drawback is the lack of LTE compatibility. There are apps that bridge this gap, and which one is right for you depends on your hardware. If your host machine is running an NVIDIA GeForce graphics card from the GTX 680 onward, you're definitely best served with Moonlight, an open-source implementation of the NVIDIA Limelight protocol that powers the SHIELD handheld's PC game streaming. Remotr works pretty well otherwise, though it has far higher latency. Both will require a little bit of setup before you can get them going, and may require you to forward some ports on your router and make exceptions in your firewall in order to stream on the go.