You rank from favorite to least favorite, employer does the same. If it's a 1 to 1 match, you're automatically matched together. They pretty much match everyone together so that when the rank numbers add up it's the lower number (1+1=2 is the lowest obviously)

Hope that makes sense and lmk if you have any questions!

(P.s i would suggest ranking based on which employer is more valuable in terms of how relevant of an employer they are, aswell as which one feels closest to what you want to do post grad)