Source: Simply Recipes
Before you start
You can make the tortillas completely by hand, by forming a thin pancake with the dough between your hands. But unless you are somewhat experienced in this method, you'll get more consistent results by using a tortilla press. These too are available in Mexican markets and come either in wood or cast iron. They are available online at Amazon.com. You can also roll out the masa with a rolling pin, between pieces of wax paper.
Making the Masa Dough
To make 16-18 tortillas, start with putting 2 cups of masa flour in a large bowl. (Hint: for added "lift" you can mix in 1/4 teaspoon of baking soda.) Add 1 1/2 to 2 cups of very warm water to the masa flour (according to the directions on the package, some brands may call for different amounts of water). Mix in and let sit for 5 minutes or so. Begin working the masa with your hands to make the dough. Work the dough for several minutes. Press the dough with your fingers and the palms of your hands as if you were kneading bread dough. If at any point through the tortilla making process the dough seems too dry or too wet, add a little more water or masa to the dough.
Take a piece of the masa dough and shape it into a ball the size of a plum, or slightly large golf ball. Make about 16-18 balls from the dough.
Pressing the Tortillas
Take two pieces of wax paper or plastic from a plastic bag and cut them to the shape of the surface of the tortilla press. Open the tortilla press and lay one piece of wax paper on the press. Place the masa ball in the center. Place another piece of wax paper over the masa ball. Gently close the press and press down, until the dough has spread to a diameter of 6 inches.
Cooking the Tortillas
Heat a griddle or a large skillet on high heat. Working one at a time, hold a tortilla in your hand, carefully removing the wax paper on each side. Allow the tortilla to rest half on your hand, and half hanging down, and gently lay the tortilla down on to the skillet. Start working on pressing the next tortilla. Cook the tortilla on the hot pan for 30 seconds to a minute on each side. The tortilla should be lightly toasted and little air pockets forming.
Remove the tortillas to a tortilla warmer lined with dish towel or paper towels, or wrap them in a dish towel to keep them warm. Serve immediately or refrigerate and reheat.
(note from Danika, I was sick of the waxed paper and I bought a tortilla maker that's a tortilla press and a cooker all in one. It was only $19.99 at stuff mart and I wouldn't trade it for the world. It is one of my few non-stick appliances that I won't get rid of.)