That's a great question. I got mine just tonight for Xmas. They're freakin great, get them no matter what, it's true apple magic all around! Even the sounds got me hyped, and they don't fall out of your ears like the regular EarPods did ALL THE TIME for me.
They seem to be connected to all devices all the time, after initial pairing. But for example when they're paired to my music app on the phone (you do it through the air play button), then when you want to listen to music on the Mac you just go to the volume menu in the menu bar and select them there, and your music will now come from your Mac. I think I was just working on my MacBook Pro, when I got a call and answered it regularely. But then I could quickly switch to the AirPods over the speakerphone button on the phone, and suddenly the sound was coming out of the pods.