Every POU can contain exactly one description worksheet.
The steps how to insert a new description worksheet are described in the topic "Worksheets: Inserting into POU".
Like code worksheets, description worksheets can be copied & pasted, moved, renamed, and deleted (see topic "Managing objects in the project tree").
The description worksheet editor provides the basic editing functions of a standard text editor:
Double-click a word to select the entire word.
Right-click selected text to open the context menu containing commands for copying, deleting, cutting, and pasting.
The 'Undo' context-menu function restores the text to how it was prior to the last editing action.