So the furnace stuff is pretty straightforward once you get the hang of it. Basically you'll need some coal and whatever ore you're trying to smelt, and the recipes arent too complicated. For your basic metals, its 5 ore plus 1 coal - copper takes about 30 minutes which isnt bad, iron needs 2 hours, and gold takes quite a while at 5 hours. Iridium is the long one, taking 8 hours, but you probably won't see much of that early on anyway.

Something interesting i found out is you can actually process quartz in there too - regular quartz takes 1.5 hours and gives you refined quartz, and if you use fire quartz, you'll get 3 refined quartz instead which is pretty nice. I usually focus on copper and iron bars first since you'll need those for upgrading your tools, and they're super helpful for crafting stuff like sprinklers later on. Just make sure you've got coal in your inventory when you're working with the furnace, learned that one the hard way!

Oh and refined quartz comes in handy for quality sprinklers and lightning rods, so don't ignore your quartz deposits when you see them in the mines. Trust me, you'll thank yourself later when you're setting up your farm automation.