Update: As some MacRumors forum members have pointed out, when pairing with an iOS device signed into your iCloud account, the step involving a button press may not be necessary. In this situation, the AirPods should be ready to pair after opening the case near an iPhone or iPad.
how to set up your new airpods
On iOS devices, go to Settings –> Bluetooth and tap “AirPods.” On a Mac, click on the Bluetooth icon in the status bar, choose AirPods, and then select “Connect.” On Apple TV, open up the Settings app, choose “Video and Audio,” scroll down to “Audio,” select “Audio Output” and choose AirPods. On iOS devices, you can also use the Now Playing widget in Control Center to select AirPods, and on Apple TV, you can hold down the Home button on the main Apple TV screen to bring up a shortcut to audio options.