Given dimensions and strength class of the concrete section and the steel grade of longitudinal bars and stirrups you can require to the program a first design of longitudinal bars and stirrups selecting the design option in Section Data dialog window (Type of calculation frame). For a rectangular column sections such dialog appears as below:
Diameters of bars (longitudinal and for stirrups) used in design are those stored in Materials Library (that you can modify as you want).
Longitudinal bars provided after the first run ("Checks" Tab selection) by present design calculation are distributed along the perimeter of the concrete regions. You can easily modify their number and diameter and run again for new checks.
After the first run in design mode the program provide only one hoop and the strictly number of cross-ties in seismic conditions ("DCM" or "DCH" ductility class). In the Stirrups-Ductility Tab window you can modify the number of hoops (one or two) and the number and the definitions of cross-ties.