Hi Anthony, if you are starting your own line of t-shirts with your own unique designs, then one thing you'll want to think about is WHO will be buying these t-shirts.
You may want to think about this part before you go any further. Who is your target market for your designs.
After you have that, then you'll need to come up with creative ways on how to REACH that target market. Some of it is going to cost money

Advertising and marketing a business costs money.
Once you have your target market figured out, you may want to figure out how much you have in your budget to spend on marketing and advertising. Even if you have the best t-shirt designs in the world, they will just sit on the shelf if nobody knows about them.
You could consider a website as part of your marketing budget. Many times, they are not as expensive as you might think, and given the returns they can give you, it can be a wise investment in your business. You may want to rethink the idea of a website:
- A website can make sales and take orders while you are sleeping!
(I have a little O'Jays wav file that plays when I make a sale in one of my stores. My wife and I will be watching a movie in the other room and she'll just smile)
- A website can answer lots of questions and be a great follow up to face to face meetings when you try to sell your shirts.
- A website can generate low cost (or free) sales by making sure your site is search engine friendly and linked well by other sites. There are some people who make the majority of their income from referrals from free natural search engine listings. This doesn't happen overnight, but with time and work, it CAN happen.
- Insert reasons 4-284 here

Once you have your target market, you can reach them by offline advertising (magazines, local events, stores), online advertising (banners on websites they visit, search enigine marketing (Google Adwords, Yahoo Search Marketing, natural search engine listings), newsletters, blogs, etc.
How to start is basically think of any and every way you can get your name out there to the people most likely to buy your product or service.