The Duplicate Text into New Clip item is available in the Text menu and via the Insert and Extract Text button on the collection toolbar when the ClipHistory tab or an AceText Collection tab is active.
Select this item, or press Shift+Ctrl+D on the keyboard, to create a new clip, using the selected part of the text of the active clip as the text for the new clip. The new clip becomes the active clip.
See Editing Clips and Text to learn how to use AceText.