Use Add Split to insert lines splitting a selected cell into smaller sections.
Steps
In the Split Cell tab of the Cell Properties dialog choose
Add Split.
Choose one of the following split types:
Vertical - Cell Height
Vertical - Subrow Height
Horizontal
Note: The option Vertical - Subrow Height is only available if the
selected cell contains several subrows. If your cell already contains a horizontal
split, you can choose whether your new vertical split will subdivide the entire
cell or just one of the subrows.
Choose a line style.
To set the position for a vertical split, enter a value as a percentage of the cell's width to place the split at
a specific horizontal position in the cell.