For those unaware, masa (done traditionally) isn't just a certain fine corn flour. It's dried, cooked in water with slaked lime, then ground and dried again. Now you have your corn+lime niacin release.
When you're ready to make some tamales, tostadas or tacos, measure out what your recipe needs, add the water, salt, oil, or lard you'll be using, and get busy.
Also use as a thickener, you'll find it in some chili recipes.