First, your going to need a special corn meal flour called Masa Harina... it's more coarsely ground than either corn meal or corn flour and it's treated with calcium hydroxide to release niacin from the corn kernel.
Then, for about 20 tortillas that average 6 to 7 inches in diameter, add 2 cups of the Masa Harina to a bowl and then add about 1 and 3/4 cups of fairly warm water and mix... it could take as much as 2 cups of water. After the initial mix let it sit for 5 to 10 minutes. Follow this with working the dough until it has a texture that will allow rolling it into balls about the size of a golf ball... say 2 inches or so in diameter.
If you have a tortillas press, the rest is easy, but if you don't, cover your working surface with a sheet of waxed paper, place a ball in the middle and cover with another sheet. Roll the tortilla out to a thickness of about 1/8 to no more than 1/4 inch thick with a rolling pin or bottle, which should yield about a 6 inch disk.
You should have a heavy skillet, cast iron is best. One should have a little real lard, but any good cooking oil will work, I suppose (I'm a purist in this, having lived in the State of Sonora for a while) and barely coat the bottom of the iron and bring it to a high heat. A drop of water dropped on the skillet will immediately "skitter" off.
Cook each tortilla no more than 30 seconds on each side, turn into a dry towel (be careful with paper since it sometimes sticks) and place in a warm oven until all are cokked.
We freeze ours and they'll keep very well for maybe two or three months.
If you like a slightly thicker tortilla, add no more than 1/4 teaspoon of making soda to the mix. (About a very small pile in a cupped palm). ...