 Re: white designes & wording not realising from the paper
Part of your problem may be the lack of understanding of the processes involved. Your printer does not have a "white ink", instead, your printer will use combinations of Cyan, Magenta, Yellow, and Black (known as "Key") or CMYK to print onto a white surface to make the full spectrum of colors (or close to). White ink is chemically a different beast, so there's usually specialized printers for making use of it.
For t-shirts there are two types of printed transfer papers that are commonly used: A transparent paper and an opaque paper
Transparent papers are usually used for white/light garments. They generally leave a soft hand and you do not need to trim nearly as much and as close as you would with an opaque transfer. The transparent method works similar to how your printer would print if the t-shirt was a colored construction paper. If the t-shirt is white, you will get the best output, the darker you get, the more you will be unable to make out the colors, and if it's a black shirt, you won't see much of anything.
Opaque transfers generally have more of a hand and needs to be trimmed close so as to not put lots of white on your garment where there shouldn't be. The opaque method works by printing onto a white powder/film, thus anywhere there is no print will actually be white when transferred to the shirt. The problem with this is that the design needs to be trimmed close, and if you are doing just lettering, you will need to print an outline around them and then cut the letters out. Think of it as using whiteout to fix a mistake, you layer the white stuff over the black, then write on top of the white.
In short, two different kinds of paper, one is only good for lighter colored shirts and has no "white", the other can be used for both but will require more time to trim to ensure you don't get extra white where you didn't want it. | 
