As part of iOS 10.3, Set Up Assistant, the wizard that walks you through signing in on a new or newly updated iPhone or iPad, will now prompt you to enable 2-factor authentication if you haven't already. Do it.
APFS is the Apple File System. It was introduced at WWDC 2016 and, starting this year, it will replace the existing file system, HFS+, on Apple Watch, Apple TV, iPhone, iPad, MacBook, iMac, and Mac Pro. So, what does that mean for you?