There should be an instruction flyer in the box.
A bolt with a plastic wingnut/knob goes through a hole in the crownstop from the bottom, than attach a slide nut to fit into a groove on the bottom of the profile.
I don't know if they still ship the same way, but 10 years ago you needed to dissassemble one of the extention profiles and re-assemble so they slide to the other side of the profile (there's a bolt with a ph3 or pz3 head on the rearside)
(But if you bought them used this shouldn't be necessary).
(If I find a link to the instructions I'll post them here)