Hi and welcome to the board. For a beginner I would HIGHLY recommend using the stabilizer method, or starch the bejeebers out of the jerseys. I meant to the point they are like card stock. Some jersey material is very light weight and may not take kindly to an iron.
A stabilizer or interfacing is an iron on product that you iron on to the back of the t-shirt so it isn't stretchy anymore. JoAnnes carries the name brand Pellon (use the featherweight one) or their own store brand.
http://www.joann.com/pellon-fusible-...FYMbHwod-M4EAg