Hi,
tables generally have the same number of columns in all rows.
So, you can create a table with initailly five columns and for those rows you only need 4 of them you merge two table cells.
Or, you simply hide the fifth colum in those rows you don't need them.
Finally you also can build a kind of tables with subforms by yourself.
This method offers more flexibility as a regular table.
For each row a subform (flowed > left to right) with all text fields etc..
And all those subforms wrapped in another subform (flowed > top to bottom).
You better don't try to combine two tables with a different number of colums.
The tables in Designer are very fragle and Designer often get's messed up by those things or crashes!