There's a few options when creating a brand:
1. Printing stuff yourself. You've got to buy or lease your equipment, which is probably out of the question if you're starting up for under a grand or two. A cheaper, and shittier, alternative would be using heat transfer printing, which is essentially using special paper you can find at Walmart and ironing it onto a shirt. Lasts around 15 washes before crackling to the point of it being unwearable, for me, at least.
2. Paying somebody else to print. That's what, from what I've seen, most low to mid scale companies(pretty much every brand on here) do this(If anybody on here prints themselves, please speak up. I'd love to hear all about the process). Find a company you can trust, with prices that leave room for profit. I'd also heavily suggest finding secondary printers and the like that you can trust, in case your primary flakes. Some people sell these sources, but, for the most part, good sources can be found by extensive Googling.
3. Printing on demand. This would include sites like Cafepress, Printfection, Redbubble, Skreened, and so on. These use methods like direct to garment printing to print their designs on, and only print a shirt when it's ordered, meaning no sitting with stagnant inventory. These sites are usually reserved for the casual 'pop culture' shirt such as this one: http://skreened.com/wellthatsjustsuper/i-m-not-saying-i-m-batman
These services are, in my opinion, no way to start a brand. You have little control over the printing process, there's no distinct branding, along with some other glaring flaws. I would not recommend it for starting out a clothing brand, rather for an artist trying to make some money on the side from selling funny shirts.
Since I'm apparently writing a small book, I might as well cover shirt blanks. There's no definite answer on shirt blanks, as they're up to target market and your personal preference. There's fitted(FUCT and SSUR) and box cut(HUF) shirts, all organic and synthetic ones. I, personally, like a box cut shirt made out of thick cotton, but you'll probably like something else. The material of the shirt matters as well, as certain printing methods won't work on certain blanks, such as with dye sublimation printing and cotton shirts. I'd highly suggest reading HTSACC's article of shirt blanks here: http://www.howtostartaclothingcompany.com/t-shirt-blanks-how-to-choose-one/
Some more required reading would definitely be Thread's Not Dead: http://threadsnotdead.com/
It covers a good amount of subjects, mostly from the viewpoint of a designer.
Reading back on this, I feel more and more like I just talked out of my ass for 3 paragraphs. If I'm wrong on anything here, somebody please correct me.