>>7136183871) Find a bunch of stones with copper ore on the surface (don't forget to mark the spots you found them at on the map for later)
2) Find clay and make a pickaxe cast and a crucible
3) Fire the the pickaxe cast and the crucible (takes almost an in-game day)
4) Smelt copper in the crucible
5) Cast the pickaxe head from molten copper (don't forget the tongues, can't hold it with bare hands)
6) Wait for the pickaxe head to solidify
It's that simple.