How would I set up a blueprint that allows a button to show text that has visibility toggled off at the start?
you will need to have a reference to the text in the widget then just have a button on clicked event which toggles visibility of the text. its actually rather simple. though you didnt mention where this text is (same widget, another widget, text render). if its in the same widget then its really easy but if its a text render in the level then it may be a bit more difficult. provide more details and i can provide a more specific answer.
edit: i assumed by button you meant a button in a widget but you may have also meant a input key so that could be another situation entirely.