After watching YouTube and reading comments from others who remained confused, it finally hit me: Excel ONLY provides "merge cell." And you don't technically need "split cell" because you can split cells already with "insert row." So the idea is to insert a row and then merge the parts that you don't want split.
Here are the steps: Insert a row, merge cells that shouldn't be split, done!
Example
Here is an example. I want to split the cells to the right of the headers that label the days of the week.
Insert Row
Since insert row inserts above the selected row, you need to select the row beneath your target. So to do Monday, I had to select the row beneath Monday.
Merge other Cells
Select the Monday cell and the cell beneath, then click on "Merge & Center" and then "Merge Cells."
Wrap-up
So Excel doesn't believe in cell division, only cell fusion. :-) And I'll have to either repeat the process more times for each day of the week or copy paste the formatting. If you want to do something different such as split cells vertically, then follow the same process but insert a column rather than a row.