Just type! You might have to type kind of slow for this to get everything, though. For backspace, you can actually press backspace, and for delete you an actually press delete (del)! Use the left/right arrow keys to move where you're typing at. Press escape (esc) to clear everything
I added calibrating, but it doesn't help much. This is my first attempt at a text engine. The font is segoe UI, so don't ask. Comment how it is! And you might notice sometimes it thinks you're still holding down a key. That is just because of how Scratch handles the shift key.