I am sorry, but I have no idea where you can find a really good summary of this article. There are a few sites that discuss it a bit, but they do not really do much to make it more understandable.
I read this article back in college myself but I'm afraid I no longer have it available to me. However, between what I remember of it and what I've read about it, let me give you a brief restatement of their main point. If you have questions, let me know.
Their main point is that race is neither 1) a real thing that can be measured objectively or 2) a complete fantasy. Instead, it is a concept that is created or constructed by society and is constantly changing.
They say that the state has a great deal to do with determining what race relations will be like and how race will be constructed. It tends to try to protect the status quo, but if there is enough pressure, it helps change things. The process of changing things (usually in a compromise between the old ways and the demands of protestors) is how "race" if formed.
I hope this is at least of some help...