First the good news -- depending on your account settings, the popup review that appears on lesson pages will either contain: (1) vocabulary from lessons you have studied, or (2) vocabulary from your private vocabulary list (you can change these settings here
). In both of these cases, answering a question incorrectly will add it to your private vocabulary list if it does not already exist, and move the word to the top of your review queue. This means that launching your flashcards should result in that word appearing with the rest of the material scheduled for review.
OK -- the bad news is it even if these words are in your vocabulary list, isn't very easy to find them if they aren't already organized by labels. This is somewhere we need to improve usability, whether it is letting people search for specific words or rank items by the number of times answered incorrectly, etc. In the meantime, if the word is totally new, you should be able to find it on the last page of your vocabulary list, since words are listed in sequential order by default at present.
Sorry if the situation is confusing, but hopefully this explanation will help until we find a more intuitive way to handle all of this stuff.