Basic question about namespaces

Hi, I'm new in kernel programming.. I'm reading the chapter about namespaces in the "Linux Kernel Networking" (Rami Rosen), but I could not find a way to create a network namespace. I understand that I should use methods like create_nsproxy(), copy_net_ns() and create_new_namespaces(), but I don't know how to set their parameters. For example, the method copy_net_ns(unsigned long flags, struct user_namespace *user_ns, struct net *old_net), defined in net_namespace.h. I know that for flags, a may use CLONE_NEWNET, but what about the other parameters, user_ns and old_net? There is a good documentation (with examples) about this? Unfortunately the book wasn't detailed enough. I appreciate any help. -- Bruno A. C. Ferreira