it should pop up a notification on your phone when you get to a text field on the aTV, but that's hit or miss.
If you're in a text field on the aTV, there should be a keyboard button in the remote app on the phone.
and it does work with password managers, so a lot of times, for things that require a user/pass to be entered in the app on the aTV itself, I can do it with a couple clicks on the phone.