Tear or cut wax paper into 2 (8-inch) squares. Add masa harina and salt to a mixing bowl and stir in enough water to hold dough together in a ball (start with 1 cup and add more as needed). The dough should be soft and just hold together, it should not feel too dry or sticky. Turn onto a working surface lightly dusted with masa harina and knead briefly to form a smooth ball.
Divide dough evenly into twelve pieces (1.55 ounces each, if using a scale) and roll each piece into a ball. Cover balls of dough with a damp paper towel while working to press and cook them.
Place a ball of dough between the two sheets of the wax paper. Press down on the dough with your hand to flatten slightly and place in the center of the press. Sandwiched in the wax paper, press the tortilla until it measures about 6 inches in diameter. (If one edge is thicker than the other, rotate and press again to even out.) Heat a dry, seasoned cast iron skillet over medium heat.
When the skillet is hot, gently remove the tortilla from the wax paper and cook in the hot skillet about 45 second on each side, until dry and browned in spots, but not stiff. Wisps of smoke may occur, check tortilla and modify heat if needed. Transfer cooked tortillas to a plate and cover with a damp paper towel. Repeat with remaining pieces of dough and by the 12th one you’ll have it down.
If you don't have a tortilla press, use the bottom of a pie plate or large pan to flatten the dough in the wax paper by pressing down with firm, even pressure.