What are mats?

I'm still new at this part and I know I'm not alone . Could someone explain mats and how they work.

mats is short for materials

materials are what is needed to enchant and or craft something like linen cloth for bandages and yada yada

Yep, just like Nyxtyr described it. Any materials required in order to craft a new item in a trade. Trade as in Leatherworking, Blacksmithing, Enchanting, Tailoring, and so on.

Materials required for leatherworking tend to be, as you might imagine, leather that you skin off beasts, and various other things, maybe thread. Enchanting tends to require materials that you can find by disenchanting items. Tailoring might use linen to craft robes, capes, and such. I think you get the idea! :)