Not only in computing but for every product, it is essential that there are instructions on how it can be used. This is the reason why every product comes with the a manual.
Help must be available for the user, for every task and subtask, they are trying to do. We can never assume, that the end user knows how to use the system.
In our prototype we have not implemented any help and documentation, yet but we are planning to add a phisical button on the kiosk machine, which will say “Help” and will open detailed help information on how to complete the current task. We will also let the user call a trained real person to assist with the kiosk usage, if needed.