First and foremost, you need a little creativity and understanding how to make designs with transparent backgrounds.
A process that uses special printers to print a design onto film, then applied to garments using a heat press.
You can order DTF from many company's (easier to start out with because you do not have to buy a DTF printer, or worry about the maintenance on the printer!
(Same day shipping from LA if ordered by 10am)
BestPriceDTF - $3.50 per foot!
Printomize America sells by the foot ($8.00!) for 22.5" wide!
If you get a Seller's Permit you can buy wholesale, but then you are required to collect Sales Tax on items sold, and submit (most likely annually to the state)