Here's what I know, but I must say I have a lot to learn about using decals. First, you choose the decal you want by browsing the textures. Type the { symbol in the texture filter. Any textures that begin with { and don't have a blue background are decals. Double click the decal you want to use. In the 3-D window, use camera mode to view the surface where you want to apply the decal. Then turn on the decal tool (shift-D) AND the pointer tool (shift-S). (The decal tool only works when BOTH of these are toggled on.) In the 3-D window the cursor now looks like a plus sign over a 2-D explosion. Place the cursor where you want the decal to be and left click the mouse. The infodecal should now be showing. For some reason the decal will show up backwards if you put it on a wall that faces north...I haven't figured out how to turn that around. Decals seem to have their own built in color, most are black, but I don't know if it's possible to change the color. I hope that helps, let me know if you have specific questions and I'll give a shot at finding the answer.