If you wish to generate a structure in cylindrical coordinates, you can select the cylindrical option.  This then allows you to space the duplication radially from the y axis, angularly about the y axis, or linearly along the y axis.  As an example, to generate a circular staircase you would first draw half of one step and then duplicate it to form the other half.

This would form one step of the staircase.

Then you would select the whole step and duplicate it to form the entire staircase.