There's a bunch of companies out there that will manufacture your designs such as Cafe Press, Zazzle, Spreadshirt, etc., although they are starting to run a little pricey for one off shirt productions. This is definitely a viable way to get your product established, as well as, see which designs work and which ones don't. It's really easy to get in over your head and purchase all sorts of equipment without truly understanding what you are getting into. I'd start with some from free e-Commerce stores and start throwing up designs and have a third party produce your shirts for you, just make sure they offer the quality you want.
Continue to research on the actual production itself, that way if you ever decide to jump in head first you have an idea of what products you need to purchase, how to set it up, etc.