The art of creating and improving weapons and armor from raw materials.
Easy way to level up smithing is:
Iron daggers only require 1 iron ingot and 1 leather strap. Thus making them the easiest item to smith and they give the same amount of exp as other items you can smith. An easy place to do this is Warmaiden's in Whiterun since the shop restocks with iron ingots and leather strips (around 15-40) every 2 days, and there is a forge right outside of the shop.
Daedric equipment is the most powerful in the game, but it also requires some of the most rare materials available. All Daedric equipment requires ebony ingots and a daedra heart to create. Large amounts of ebony ore can be found in Gloombound Mine, roughly east-southeast of Windhelm. The mine has 16 ebony ore veins. This leads to about 40 ebony ore per mining run, (plus many high-quality jewels) which makes enough ingots to create a full daedric or ebony set plus some upgrades (ores seem to respawn in mines about once every in-game month.) Daedric hearts are harder to find. There is a chance for all alchemy and general shop owners to sell some, although their inventories don't restock very often. There is one in the companions guild, in the lower level inside Kodlak's room. It is on the desk outside of his bedroom on a plate. It will respawn about once a week. The best place by far to get them though is at the Shrine of Mehrunes Dagon. This location is found during the quest started by visiting the museum of the Mythic Dawn in Dawnstar. 2 Daedra will spawn inside and outside of the shrine after 1-2 weeks (all the items found in the shrine, including gold ingots, soul gems, and various enchanted items will respawn with the Daedra.) The Daedra can then be looted for their hearts and various other goodies.