Last May, Apple caused some controversy in the gaming community when it rejected Valve’s Steam Link app from the App Store merely a day after Valve announced it. Steam Link is now back for the iPhone, iPad, and Apple TV, though, and you can download it through this link for iOS.
Steam Link is a free app lets you stream games from your PC or Mac to your iOS device or Apple TV, so long as you’re on the same network. (You also don’t need the physical Steam Link hardware to do this.) You can do this over Wi-Fi, but Valve itself says you’ll be best served if your computer is hooked up to an ethernet cable. You should also keep your iOS device close to your router for the best performance.