An operating unit is used to choose least alphanumeric characters and/or symbols and to combine them to form a character group. A display device displays selectable characters in a selection field and displays selected characters in an one input field. Data is stored in a storage unit. A data processing unit selects data from the data stored in the storage unit according to predefinable criteria, taking into consideration a chosen character and previously selected characters. A completion suggestion with at least one completion element is displayed in close proximity to the chosen character in the selection field, insofar as a possible completion of the chosen character and the previously selected characters. The completion element is choosable by a user by the operating unit, and a chosen completion element can be selected by a user by the operating unit.