Tamiya instructions are usually pretty good. It will tell you what you need to do, though you may have to hunt it up. They're complete, but not always in the most intuitive order or don't explain things very directly, especially when it comes to painting. I am unfamiliar with this particular car, so I can't tell you what to do. You'll have to paint it some color, wether it's white or blue, because decals don't stick well to bare plastic. Tamiya does things different ways every time, so you may paint it white and use the blue decals, or mask it and paint the blue parts, or even a combination of the two. Just read, and reread the instructions carefully. It's in there. Hopefully someone can come along and help you better than I.
Also, this should be in the main "Car Modeling" section, when you get started you can show us what you're doing here. I can't wait to see it.