Masa flour is available in two varieties. The one marked, "For Tamales" will work, but isn't your best choice for tortillas, whereas the regular Masa flour will work just fine for tamales. Think of it as the difference between plain and self-rising flour. You want the regular stuff. This is a good time to mention this is not cornmeal, or cornflour (cornstarch). Go to a Latin market for this-it will be fresher than what sits on the shelf at a large grocer. You can purchase bags of already mixed masa harina, but that's really lazy as it is just flour and water.
Here's what you do:
Start with a small batch-this will make about 8 regular sized tortillas, or 12 minis. I don't bother with minis-we're more of a maxi sort of family.
You'll need 2 cups of masa flour, and about 1 1/2 cups warm, not hot water. Add the water slowly, until you have it come together. The flour will take a surprising amount of water, so keep adding it a bit at a time until the dough feels spongy. A good test is to take some, roll it into a ball, then smash it against a cutting board. If the sides crumble (some cracking is expected) you need more water. Be careful though, as you won't be able to roll dough that is too wet either.
Begin heating your griddle. I use a cast iron pan set over medium heat, but you are the best judge of what will work best for you. It will smoke a bit, so you may wish to put on a fan, or open a window.
Divide dough into 8 pieces, keeping the dough you're not working under a damp towel. I roll between wax paper sheets, but cling film works too. Don't worry about the edges being perfect, you can always trim them with kitchen scissors afterward if you really care. No one is going to see that if you're making enchiladas.
Cook about 1 minute, or until lightly browned on the underside, then flip and bake another 30-45 seconds. Sometimes they will puff, which is a good sign you're done. If not, just look for the surface to dry out a bit.
And that's it. Flour and water, a rolling pin, and a frying pan. I know you can do that. I can't be responsible if you decide to deep fry them, but ...if you do, mix cumin, chili powder, and some cheese powder from a packet of macaroni cheese and sprinkle it over them as soon as they come out to drain. There's your Dorito's craving, sorted. You're welcome.