This is a pretty neat walkthrough of how to use the loop recorder in Traktor Pro 2.
Created by Dubspot Instructor and Traktor DJ Extrordinaire; The infamous DJ Shiftee.
1. By clicking the Deck letters you can switch modes for the decks between (Track, Sample, External). This saves you the trouble of going into the setup. :)
2. After creating a loop in the loop recorder, you can drag the loop in to a sample deck.