The vast majority of corn tortillas you will find in markets in the United States are made using rehydrated corn flour, such as maseca.
This is definitely the easiest way to make them. However a handful of places in the United States make corn tortillas the traditional way, using an ancient process called nixtamalization. Scientists believe people living in central Mexico developed corn at least 7000 years ago from a grass. Nixtamalization was first developed in Mesoamerica, which is the central region of America, from central Mexico to Costa Rica to the mountains of Peru, but it was also practiced by Native Americans in North America, from the plains of Texas to the valleys of Vermont in New England.
In corn nixtamalization the corn kernel is soaked and cooked in a lime solution which removes removes the skin of the kernel and produces a softer dough than unprocessed ground corn. Corn can be nixtamalized to produce a variety of products including masa, hominy, and tortilla chips.