The sidebar widget can be added and customized like any other widget by dragging it from the list of available widgets to the position, you want it to be in (depends on theme) inside “Appearance” -> “Widgets”.

The title and submit button text can be changed in the widget settings and it uses the confirmation messages from the general plugin settings. By default only an email field is shown but you can load a different template.

A suggestion for a sidebar template with fields fir lastname, firstname, working with ADC is: