You can access Control Center from any screen on your iPhone and iPad, including while you’re in an app or playing a game. However, the procedure has been tweaked a bit in iOS 11.
On most iPhones, as in previous versions of the operating system, you swipe your finger from the bottom of your screen upward. Make sure that you start at the bottom edge of the screen.
The procedure is different for an iPhone X or iPad. On the former, you must pull down from the top right corner of the screen.
On the iPad, the Control Center is located alongside the multitasking switcher and has repurposed the basic flick-up-from-bottom gesture for displaying the Dock. Now you must swipe ALL the way from the bottom of the screen to the top to summon the Control Center.
As before, you can use the Control Center to switch songs, toggle airplane mode, turn on flashlight mode, etc.