Copper Ingot is used to create tier 1 tools and armour but it is a bit better.
You can obtain Copper Ingots by smelting a Copper Ore in a regular furnace.
The main purpose of Copper Ingots is the crafting of bronze, as bronze is one tier higher then copper. A Bronze Ingot can be crafted in a regular crafting table combining 1 Copper Ingot with 1 Tin Ingot (Shapeless), you will then get 2 Bronze Ingots.
To craft a Copper Shovel, Copper Hoe, Copper Axe or Copper Pickaxe (or a Copper Sword aswell in the pre-1.8 Soul Forest Mod versions) you can just use the regular crafting recipes but instead of a normal "Iron Ingot" you use a Copper Ingot.
In pre-1.8 Soul Forest Mod you can also still craft a Copper Armour, to do that you also use the regular crafting recipe of every armour piece but instead of "Iron Ingots" you use Copper Ingots.
Last but not least you can also craft Copper Blocks by combining 9x Copper Ingots in a regular crafting table.