A simple description with two photos is found under the heading of "Attaching the Cable to the Tow Vehicle" at the end of eTrailer's article about installing a breakaway system
(you don't need the installation, just that last section).
I note that they don't use any kind of additional clip, so they must pull the plug out of the switch end to hook up the cable - I don't think many people actually do that, but if you do, finish (put the plug back in) before plugging in the electrical cable, since some brake controllers apparently don't like being exposed to the 12V due to the breakaway switch being activated like this.
eTrailer's videos are oriented to products (e.g. brake controller), rather than to activities (e.g. hooking up), but you might find something among their video collection