1. Mix and knead masa harina and water until the dough comes together.
2. Divide and shape the dough into 12 balls. Lay a clean, damp dishtowel over the balls of dough while you press the tortillas.
3. Heat a heavy skillet or griddle, ungreased, over medium heat.
4. Use a tortilla press or a heavy pie plate to press each ball of dough very flat. Transfer to the heated pan and cook until little spots appear on each surface, turning once (30 seconds per side). Repeat until all tortillas have been cooked. Let cool until flexible (5 minutes) and fill as desired to serve.