Tin Ore is one of the new ores added by the Soul Forest Mod. Tin ore can be found in the overworld together with a few of the other Soul Forest Mod's ores. Tin Ore is a low tier ore and can be mined easily with a wooden pickaxe or better. It can usally be found in large veins underneath layer 100 in any overworld biome.
Tin Ore can easily be smelted into a Tin Ingot in a regular furnace.
The main purpose of tin is the crafting of bronze, as bronze is one tier higher then tin. A Bronze Ingot can be crafted in a regular crafting table combining 1 Tin Ingot with 1 Copper Ingot (Shapeless), you will then get 2 Bronze Ingots.
Even though you can easily craft Bronze Ingots using tin, tin can also be crafted into its own set of tools (before release 1.8 Tin Armour & Tin Sword are still in the Soul Forest Mod).
To craft a Tin Shovel, Tin Hoe, Tin Axe or Tin Pickaxe (or a Tin 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 Tin Ingot.
In pre-1.8 Soul Forest Mod you can also still craft a Tin Armour, to do that you also use the regular crafting recipe of every armour piece but instead of "Iron Ingots" you use Tin Ingots.