I'm still new to much of this, and I'm not sure if this is what you're asking for, but I think what you're trying to do, regarding playlist organization at least, can be achieved by clicking the checkboxes next to the words in your master vocabulary list, then clicking "Review." This will allow you to review only your checked words. If you wish to save your selected words for later in their own list, go to the "Action…" dropdown menu and select "label checked," and assign it whatever label you want. The name of that list will now appear in the "show all vocabulary" dropdown. It's a sort of tag system, but it's kind of cumbersome--to delete your list, you'd have to delete the words from your vocabulary list altogether--so I haven't used it much. Is that what you're looking for?