Instead of swimming with paddles, the fists drill is more like swimming with anti-paddles. Just as the name implies, close up your hands into fists and swim.
If you feel like you aren’t getting very far, remember to keep your elbow high during the pull phase of the stroke. Let your arm seek out the optimal position that grips the water and provides the most power.
If you have a tendency to drop your elbow and let your arm slip through the water, this drill will provide the feedback you need to develop a better ‘feel’ for proper arm positioning during your stroke.