First, add the masa harina and lard to a medium sized bowl. Use your fingers to break up the lard and thoroughly coat the pieces as they get smaller, until you have a sandy, uniform mixture. Next, fill a measuring cup with the warm water and pour in half of it into the bowl, loosely mixing the mixture a bit with a fork. Then, add the salt to the remaining water and stir until the salt dissolves fully.
Add the water mixture to the bowl and use a fork to mix everything together until the water is absorbed and it starts to clump together. At this point you can begin mixing with your hands until the dough fully combines and comes away from the sides of the bowl. It should feel like brand new playdough when done. If it feels a little dry add water ½tbsp (7.5ml) at a time. The dough should be hydrated, but not sticky. It should not feel like it's leaving any residue on your hands.
Wrap or cover with a damp cloth, and let it rest for 30 minutes. Setup your workstation at your stovetop. Then, divide the dough into 12 equal pieces (roughly 38.5g each) and re-cover. Turn on your burner and heat a non-stick pan with at least 10in (25cm) of flat surface to medium-high heat (see notes). It's preferable to use a griddle-like pan that can take relatively high heat for an extended period of time.
While that is heating up, you can shape one of the dough balls using a tortilla press. First, cut a plastic bag down the sides from top to bottom and place a dough ball in between the layers. (see notes for other options than a single-use bag). Press the dough into a tortilla and peel the flattened dough away from the plastic like a sticker.
Take the tortilla and lay it into the pan to cook for 30 seconds. Quickly flip the tortilla over and cook for another 30-60 seconds. The tortilla should begin to smell like roasted corn. Now, flip the tortilla back to the other side and cook for another 30 seconds. If your pan is heated properly and the first sear worked, the tortilla will begin to puff up. You can promote puffing by lightly tapping the center of the tortilla during the final cook. Sometimes there are weak spots which release the steam that should make your tortillas puff. Try pressing down on the hole with your spatula to seal the steam back in and promote inflation.
Adjust your pan temperature after the first tortilla depending on how slowly or quickly it cooks. Place the tortilla into a warmer or on a plate with a towel or paper towel over it. Repeat the process for all 12 tortillas.