Tin is a metal resource added by IC² and generated as ore between layers 0 and 40, usually in groups of up to 6 blocks. It requires a stone pickaxe or better to mine.
These forms of tin are seen during ore processing:
These forms of tin are seen during metal shaping:
Although not quite as prevalent as copper, tin is still a staple material of IC². Note, however, that tin plates and item casings have mostly taken over the position ingots used to occupy in pre-experimental crafting recipes (as with most other metals).
Starting off, tin will mostly go towards crafting RE Batteries and Tin Cables. Later on, a fair amount will likely be used for Universal Fluid Cells, Electric Motors, Mixed Metal Ingots, and nuclear reactor components. (Don't forget about Tin Cans to conveniently store your food!)
Unsmelted tin can also be mixed with copper in a 3:1 ratio (copper:tin) to produce Bronze Dust.
Basic crafting is the same for (almost) every metal. Any pre-ingot form, except for the Tiny Pile of Tin Dust, can be smelted into an ingot.
Smelting anything but dust is a waste of resources, though - check the ore processing page to see how to maximize your output.
9 ingots craft into a block and vice versa.
Dust comes from 9 small piles, but you can't craft small piles out of a single dust like you can craft ingots out of a block.
For parts that you make using this metal, plates and item casings and so forth, there's a page for that already.