According to MKBHD’s video, you just look at the key you want on the on-screen keyboard and then click it by touching your thumb and index finger. They also mentioned in the keynote you can connect a Bluetooth keyboard and type on that.
This has been used on many other devices and is miserable, it's like using the joystick to type on a game console
it sounds kind of exhausting, but i guess have to try it to know for sure.