The tool is basically a socket. It becomes more clear with the boot removed.
The u-shaped insert slips onto the body of the inner tierod like an open end wrench. The large part of the tool goes on over the threaded end of the inner tie rod (with the outer tie rod removed) and interlocks with the u-shaped insert. Then you just use a ratchet and turn that like a socket.
Adding a short video from youtube.
