It's important to understand that these things are plastic transfers, and NOT a method for transfering ink onto the material. What you end up with is a layer of very thin plasctic stuck tot he shirt. The transfer used in the pictures is meant for white tee shirts, and is a clear material. The printing is done on the underside, in reverse. This means that when you put the transfer on the shirt, with the backing paper uppermost, the printed side is next to the shirt material, and basically viewed in reverse through the transfer material.
There is a 'Dark tee shirt transfer' product also on sale, and whilst this is very similar, the transfer material is opaque white, and the printing is done on the top side without being reversed. this stuff is useful for covering up cock-ups.

Yes I made one...........
At all times follow the instructions given, but remember that once you iron the stuff on, it's bloody hard to get it off, and will usually wreck the shirt!!!!!!!