This program is an ugly, C-like Rust translation of the C example at the bottom of man 2 clone with some extra additions to launch a namespaced bash process. The particularly tricky bit is to remember to set the uid/gid maps correctly after cloning the process (see man user_namespaces), otherwise stuff like chroot won't work. For more about namespaces, see Michael Kerrisk's Namespaces in Operation series.
Usage of the program requires two arguments: a hostname and a chroot path.
There are many resources out there on establishing a chroot. If you're on debian/ubuntu distros try sudo debootstrap stable <chroot_path>.