Try this link, has basics:

http://www.bare-metal.com/Experts-Choice-Decal-Film.html

 

If you mean the liquid decal film try here:

http://www.bare-metal.com/Microscale-Model-Finishing-Products.html

I buy Testor's Decal Paper at Hobby Lobby, both white and clear backgrounds..  I make the decal art in MS Paint (Don't have anything fancier, like Photoshop) and then print it (inkjet) on the decal paper.  Once that's done, I then spray it with Testor's Decal Bonder and I'm done.  Just make REALLY sure you don't get any bonder on the back of the paper where the artwork is, or you'll lock it into the paper forever... Several light coats is what you want to apply, not one heavy, wet coat...