....? why would you need a video...?
Heat 2 Copper Ingots
Or
Heat 2 Any other Metal ingots
Place on anvil while they have the "heated" status
Use the Radial menu to ensure Blunts are chosen
Hammer it into a small hammer head.
(Must look like a hammer head for the Blacksmith to make use of it, but a customer will buy it regardless of type (mace/etc)
Take head, cool it in the oil, place it on the Workbench, attach a one-hand Grip to it
You're Done. (When you attach the grip with a cooled head, it will tell you in the bottom corner that you created the item) (All items that Customers will purchase will give you a notification in the bottom corner, If they don't give the notification, You didn't do it right, and it isn't saleable.)
The Blacksmith can use only small hammer head, but they can use one or two hand grips for it. But Only one hand works for Customers.
Large Hammer is done with 3 heated ingots.
When making a weapon, all ingots must match, You can't have 1 tin, 1 iron, and 1 copper, that won't do diddly.
Large hammer uses a 2h grip, same overall process as above.