If you're going to switch from an apple device to an an apple device, you want to bring along as much of the data from your phone as you can. While plugging in a cable is a solution that can be walked through, it's not the only one that you can use.
You need the link to dig it up, because it's unlisted in the App Store. It may be a little while before you can actually use the app, but it is starting to roll out to the public. Ivy Hunt told The Verge that the roll out should be complete in a few weeks. We are waiting for an update to the devices that will allow them to work with the app. The app will be available in the markets where the phones are sold once the devices are ready.
Once it's active, the switch toandroid app will be able to initiate the transfer process by popping up a qr code on the phone, which your phone can use to load photos, videos, contacts, and calendar events.
You would be correct in assuming that it should work with other devices, but at first the only phones it works with are the Pixels. There is no word on when it will be ready for other phones.