To add a column, click the plus button that is right of the last column of the table. A new column will be added. A new column always has the name
New Column. You can click on the column header to edit the name of the column.
To delete a column, open a column header and click Delete option.
To change the visibility of a column, click the Toggle button found in the upper right hand corner. You will see a switch button for every column. Toggle the switch to hide the column. Toggle it again to display it.
Resize by dragging
Hover your mouse near the right border of the column header. An indicator will appear. Hold your mosue down and drag to resize the column.
Hover your mouse between two column headers. An indicator will appear. Double click the indicator to resize the column to the max size of its content.