You can insert rows and columns using a number of different methods.
The new cells have the same formatting as the text in the row in which the insertion point was placed.
The new cells have the same formatting as the text in the column in which the insertion point was placed.
New rows are added to the bottom of the table; new columns are added to the right side of the table.
When adding columns, if you drag more than one and one‑half times the width of the column being dragged, new columns are added that have the same width as the original column. If you drag to insert only one column, that column can have a narrower or wider width than the column from where you dragged. The same behavior is true of rows, unless the Row Height for the row being dragged is set to At Least. In this case, if you drag to create only one row, InDesign will resize the new row, if necessary, so that it’s tall enough to contain text.