Hi Looky
You can't.
A column is a column with a column letter or column number identifier and
cannot be split.
You can give the "appearance" of a split column, by having a number of cells
set as Merged, with the cells below not being Merged.
I would STRONGLY advise against ever using Merged cells - it will come back
to bite you at some stage.
Instead, choose Format>Cells>Alignment>Horizontal>Center across selection
This will give the same "appearance", without the other pitfalls of merged
cells.