You can enter or exit column mode by pressing "Alt + C" or selecting "Column mode" in the edit menu. In column mode the font has to be a fixed-width font, like "Consolas" or "Courier New". The current font is temporary changed if necessary.
Edit text in column mode
First position the text cursor where you want to edit text. Then select several rows by e.g. pressing "Shift + DownArrow" or using the mouse. You can either select several columns or no columns at all.
Put the text cursor after the "x" on line 2 and press "Shift+Down" twice. Type "y".
"y" is inserted at every selected line.
Select x on line 2 - 4. Type "y"
The "x":s are replaced by "y".
Most other editing features can be used as well, e.g. backspace, delete...
Special column mode features
There are some functions in the "Edit -> Column" menu.
Insert or overwrite entered text at every selected line. You can do the exact thing manually as described above.
Clear the selection by overwriting with blank space characters.
Get some statistical data on selected numbers. Please note that the selection should only contain numbers and not text.
Sort functions are available in the "Format" menu or in the editor context menu. You can use this in column mode to sort only a selected column, instead of the entire rows.
Select a column to sort and select "Ascending sort" in the "Format" menu.
The values in the selected column are now sorted.