"A Roux is a paste of butter and flour that is used to thicken almost everything in Western cooking. A white roux is the base for white, or cream sauces, such as sauce béchamel, used with chicken, vegetables and fish. A brown roux is the base for much cajun creole cooking and for many rich casseroles."Cooksrecipes.com
The time allowed for the cooking determines the basic flavor and color of the roux. What is necessary to remember is that the roux can burn very easily. Simply start with 1/2 a stick of butter and melt it and then add some saucing flour. You will know when you have the correct amount of flour , as the roux will have a sheen to it, but will not be a lumpy paste. Stir the roux with a fork or a small whisk the entire time to keep lumps from forming. Then just keep whisking occasionally while the roux cooks. It will get darker as it cooks, and depending on the type of sauce that you are creating you'll need to watch for it's doneness. I use a roux as the base for almost everything from cheese sauce and soup to gravy. It's a wonderful technique to learn and it only takes a couple of tries to perfect. When the roux is done, the liquid ingredients are added to it, (cream, milk, broth etc.) and the flavouring ingredients (cheese, seasonings,meat ,vegetables etc.) are added last.