A viewport is created when a sheet is divided up with split bars. Each viewport column (column of viewports) has its own horizontal scroll bar. Each viewport row (row of viewports) has its own vertical scroll bar. For more information on viewports, refer to Customizing Viewports.

You must add an entire viewport row or viewport column; you cannot add an individual viewport.

The viewport column and viewport row indexes are zero-based, so the first (leftmost) viewport column and first (top) viewport row both have indexes of 0.

Typically, the first method is for single-sheet solutions and the second method is for multiple-sheet solutions.

Reference

FpSpread Class
FpSpread Members
RemoveViewport Method