You must use a Heat Press! Each press is a little different. Use temperatures from 380-400 degrees and press for 45-60 secs. I recommend using a test shirt and a test print with your press to see what temperatures and times work the best on your specific press.
*You will need to use light colored shirts which must be at least 50% polyester. Sublimation ink only binds to polyester, so the higher the polyester count is, the more clear your image will be.
**ADVICE** Butcher paper, card stock, computer paper, and teflon sheets are all things that can be used to be put in between and on top of your shirt to prevent ink from getting on your heat press or the back of your shirt.