Salvage is a child skill that allows you to get materials from tools/armor you salvage with it.
Experience gain for child skills such as Salvage is different from normal skills, because it's a child skill it's not possible ot level it up by using it. The level is instead determined by taking the average from the two parent skills (repair and fishing by default).
Salvage does not currently have a super ability.
Unlocks at Salvage level 35 by default When unlocked, this ability allows you to salvage damaged items. The yield percentage increases as you level up. A higher yield means that you can get more materials back. With advanced salvage you will always get 1 material back, unless the item is too damaged. So you don't have to worry about destroying items without getting anything in return. To illustrate how this works, here's an example: Let's say we salvage a gold pickaxe which is damaged for 20%, this means that the maximum amount you could get is only 2 (because the pick is crafted with 3 ingots - each worth 33,33% durability) which is equal to 66%. If your yield percentage is below 66% you are not able to get 2 ingots. If it is above this value you are able to gain the "full amount", which means that you will get 2 ingots.
Unlocks at Salvage level 2 by default This ability allows you to get enchanted books when salvaging enchanted items. Depending on your level the chance of successfully extracting a full or partial enchantment varies. When an enchantment is partially extracted, the enchantment book will have a lower level enchantment compared to what it was on the item.