If no part of the active file has been selected, Extra|Sort Alphabetically will sort the entire file alphabetically, paragraph by paragraph.
To sort the entire file on a specific column of text, select that column of text before selecting Extra|Sort Alphabetically first. Make sure that the selection does not span more than one paragraph. All the paragraphs in the file will be sorted, using the selected column as the sort key.
If the selection spans more than one paragraph, then the selected paragraphs will be sorted. If you want to sort only a selected number of paragraphs on a certain column, make a rectangular selection first. The paragraphs that are partially covered by the rectangular selection will be sorted entirely as if the selection was a normal one. However, the sort order will not be determined by their entire paragraph text, but only by the text covered by the selection.
If you are working with a text files that contains information arranged in columns, padded with spaces, you could make a rectangular selection of the third column and then use Extra|Sort Alphabetically. The data will then be sorted on the third column.
The progress meter indicates the percentage of paragraphs that have already been sorted. The sort operation works from top to bottom. If you abort the operation, the paragraphs that have already been sorted will remain sorted, and the unsorted paragraphs will maintain their old position. If you want to cancel the sort altogether and revert its results, use Edit|Undo.
Extra|Sort Alphabetically Z-A