The best way to do it right is to go  to youtube and search for 

heat transfer vinyl with a home Iron

However here is the step by step instruction

1. Place a garment on a hard flat surface and smooth out all the creases and wrinkles.

2. preheat iron to cotton settings and swith off the steaming.

3. place your graphics the way you want it on the garment (make sure it is the right way round - transfer film needs to on the to and design needs to touch the fabric) and cover it up with the silicone paper or baking paper

4. apply firm preasure to heat in the design into a fabric (applypreasure for about 15-20 seconds on every part of the design)

 5. try to peel of the transfer film slowly and carefully and watch if the vinyl stay with the fabric. If it does not (the design comes of with the transfer film heat it in for another 15-20 seconds on this spot)