You can edit these properties using the mouse and keyboard. The length property will be enabled depending on the datatype. Select different rows in the list to view extended properties in the column properties area.
To add a new column to the table enter a column name in the blank row at the bottom of the list. Move the new column up and down the list using the toolbar arrow buttons 
.
See Also
Table Design
Table Design (Toolbar)
Table Design (Column Properties)
Table Design (Table Properties)