Cut the red onion into half rings, squeeze out the garlic, mix everything.
For the marinade, type a glass of hot (but not boiling, otherwise the onion will cook) water, add salt, sugar and vinegar. I used wine, but given the ratio of water and vinegar, I assume that the table can be taken in the same volume.
Mix thoroughly and fill the mold with onion-garlic, the water should cover them completely, if not enough, just add more hot water.
Close the lid, leave to marinate for an hour.