//Set the worksheet where you need to add the column
ExcelWorksheet xlsWorksheet = (ExcelWorksheet)xls.easy_getSheetAt(0);
ExcelTable xlsTable = xlsWorksheet.easy_getExcelTable();

//Create the new column (the column stores only the formatting, not the data)
int nNewColumnIndex = 1;
ExcelColumn xlsNewColumn = new ExcelColumn();
xlsNewColumn.setWidth(200);//optional
xlsTable.easy_insertColumn(nNewColumnIndex, xlsNewColumn);

//Add data for the new column
ExcelCell xlsNewValue;
for (int nRow=0; nRow<xlsTable.RowCount(); nRow++)
{
      xlsNewValue = new ExcelCell();
      xlsNewValue.setValue("new value for row " + (nRow+1));
      xlsTable.easy_getRowAt(nRow).easy_insertCellAt(xlsNewValue, nNewColumnIndex);
}