We have the purple molecules and we have these orange molecules. Now, let's say on the outside of the membrane, we have a high concentration of these purple molecules and a high concentration of these orange molecules. On the inside, we have a low concentration of the purple and a low concentration of these orange molecules. Now, what this antiporter basically does is it allows these purple molecules to naturally move down its electrochemical gradient. So from the high concentration to the low concentration. And this doesn't actually require energy.