When that is already a problem for you, you should ask yourself if you really need GTK. Do you have already much experience with GTK? You may know that GTK community is not very active currently, so it is very difficult to get help. The Krause book is only for GTK2, and the online API docs are fine, but it takes some time to read and understand it.
And try to get the Dom book, I think you are the target audience. I already answered you in IRC -- contact Manning and ask how you can get the book in your country, 20$ is really not that expensive.. We should find a way. And read the Tutorial, it is really fine. For your question: TOPLEVEL flag is the default for newWindow(), so you do not need it. And when you want it, GTK3 flags are pure, so the identifier is WindowType.TOPLEVEL.
