Problem with assembly of trailer coupling

Hi people I’m new here and I have to say right away I like it nice and often found solutions for my problems here just thisma net^^ And I do have a great problem. I ordered a Ahk from my parents at ramader(or as it’s called :-D) for the Opel Omega B step-neck because I need something. So now I think I’m building this thing myself can’t be that hard. And now I want to ask if someone has ever done this of you or knows how to do it. I can’t even imagine how this should look like. If the plate is to be screwed in its trunk or somehow under the car the rest of it wouldn’t be a problem then all you have to do is screw it in to this base plate and because the hook up and the electrics. Only I just don’t know how this plate gets to the car.. Would be really nice if someone could help me explain that for a moment. Hope you can help me. Thank you. Greeting fred