Help > Authoring > Working with Tables > Table Editing > Inserting and Deleting Cells > To Add a Cell to a Non-Custom Table:
  
To Add a Cell to a Non-Custom Table:
1. To add a cell, place the cursor in a cell and choose Table > Insert > Cells.
2. In the Insert Cells dialog, select one of Shift cells left, Shift cells right, Shift cells up, or Shift cells down. The cell containing the cursor moves in the direction specified and a new cell is inserted. Empty cells ares inserted at the end of any other rows in the table when the shift is left or right or at the bottom of any other columns when the shift is up or down.
If more than one cell is selected, the selected cells move in the direction specified and the new cell inserted.