Put the masa harina in a bowl and mix in the salt. Add about 1 cup warm water and mix with your hands; add more water as needed until the dough comes together. Knead for a few minutes to smooth the dough out. The dough should be firm and springy and should not stick to your hands. Test by forming a small disk, if it cracks around the edges you need more water.
Place a piece of heavy plastic (like from a garbage bag) onto a tortilla press. Form a 1 1/2-inch ball of dough and place it in the center of the press. Top with another piece of plastic, close the press, and push the lever down to form the tortilla. (Alternately, the dough balls can be rolled between plastic sheets with a rolling pin.) Open the press and remove the top layer of plastic. Carefully peel the tortilla off the bottom plastic and place it onto a hot, ungreased cast iron skillet; cook for about 1 to 2 minutes per side. Remove the tortilla and place it on a clean tea towel; keep it covered to keep it soft and pliable. Continue until you have used up all the dough.