The host side drives a USB device instead of being one.

It talks USB/IP itself, so it needs no kernel driver, no vhci and no root - serve a device in one process and drive it from another, on any OS. The device can be virtual (either library) or genuine hardware exported by a real usbipd.

Three ways in, from most to least code you write:

Host driver - the native libusb-shaped API: open a device, run control/bulk/interrupt/iso transfers.
pyusb - code already written against pyusb drives a virtual device by loading the libusb wrapper as its backend.
Wrappers - an already-compiled binary (dfu-util, lsusb, a WinUSB app) runs unmodified against a virtual device.

In USB/IP terms this side is the client (role table) - something must already be serving before any host call can succeed.