When you went to a Roman market, you could buy a number of things. Food, trinkets, and of course, curse tablets.
Once you'd purchased your tablet, you had to come up with your message, which was generally hilarious. You addressed a god, and then labeled your curse (often as a memorandum, seriously), identified the cursee, told the god their offense, and then asked for their grief or blood or small intestine or whatever.
After you were done writing the curse, you folded the tablet over and effectively scrambled the contents into the most aggressive word search ever. This was supposed to obscure the contents from the psychic vision of the cursee, and bring it closer to the god. If you were feeling particularly ambitious you could put some hair or pins inside; one discovered tablet had seven nails hammered through it. (Do NOT mess with seven-nail guy.)