Okay, let's get all geeky on tamales today. If you are going to to to all the trouble to make tamales at home, you probably want to start out with fresh masa. No, not fresh from powdered, really fresh. Which brings up the question: What is masa exactly?
Masa is a dough made from nixtamalized corn. Nixtamalization is the process by which dried corn is broken down chemically. The word "nixtamal" comes from the words for ash and corn. In ancient Mesoamerica, dried corn was boiled with wood ash to nixtamalize it. Slaked lime (calcium hydroxide) is the modern substitute for wood ash.
The whole thing sounds a lot more complicated than it really is, as this video from the CIA San Antonio demonstrates.
So after you watch the CIA video, and assuming you don't have a stone mill at your house, the next question has to be: Where can I get some fresh masa?
Allow me to recommend Mi Tienda in Pasadena. Here's a holiday tamale-making video I made about the place four years ago. Excuse my Tex-Mex Spanish.