Through the leech cringle
Usually, the reef line doesn't get attached directly to the grommet (cringle). It should come out of the boom, through the cringle, and back down to the boom. Look for a little eye or a bail or some other attachment point on the boom there. That same line should come out of the front end of the boom, and you should have some way of securing it there (like a cleat).The line does nothing with the rams horns. When you lower the sail to reef, hook the grommet on the leading edge of the sail (the luff cringle) on one of the rams horns. Then pull on the line coming out the front of the boom and it will pull the leech down to the boom. Cleat it, harden the halyard and you're done.You can lace sail ties through the other grommets, but that's just for neatness. I'll do it if I reef at the dock or if I'm close hauled, but if the boom is out of reach I don't bother.