Help > Authoring > Working with Tables > Table Editing > Adding Rows and Columns > To Add Columns to a Table:
  
To Add Columns to a Table:
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Column operations are not applicable to custom tables.
The following rules apply when adding columns to a table:
When inserting single columns, the attributes for the new column are copied from the column containing the cursor.
If you have more than one column selected when you add new columns, the same number of columns will be inserted. The attributes for the new columns are copied from the right-most column of the current selection for Insert Column Right, or the left-most column of the selection for Insert Column Left.
1. To add a single column, choose Table > Insert > Column Right or Table > Insert > Column Left.
2. To add multiple rows and columns to your table simultaneously choose Table > Insert > Rows and Columns.