what's the actual way to make copper golem?

Once it's built, the point of it is sorting. It takes items out of copper chests and carries them to ordinary chests nearby that already hold the same item - so put one of each thing in the chests you want it to fill, otherwise it wanders about not knowing where anything goes.

place a block of copper down and put a carved pumpkin on top of it, pumpkin last. that's the whole thing - the videos differ because a jack o'lantern works just as well as the pumpkin, and the shape can go sideways or upside down as long as the pumpkin is the block you place last. the copper block turns into a copper chest when it spawns, which threw me the first time. it oxidises as it runs and eventually seizes up into a statue, so wax it with honeycomb if you want it left alone.