Custom Text fields can be added by clicking on the big + button in the Field manager, on both Organization and Event levels, and selecting the option Text in the dropdown offered.
Planners can edit the name of the field (e.i. Participant name), label for the field visible to contacts and participants (e.i. What is your name?) and the category the field belongs to (e.i. Personal information).
Field can be further customized by selecting the minimum and maximum number of characters that can be used for this field, as well as what might be the default value for this field.