Vita is interpreted mostly as the means by which sorcerers practice their craft, but equally it is what blacksmiths and scholars, and everyone else, use, in their own way, to practice their own crafts. The difference is that most people don�t realise that the part Vita plays in their normal everyday tasks.
You cannot normally see Vita (with the exception of the Initium Occasus), but its effects are often quite visible, and its presence can be felt everywhere. Everybody, Human and Nephilim, animal and plant, has the potential to tap into Vita and use it to their own means, but only a handful of Humans have achieved this; these are the Humans who have managed to develop Aptitudes. Nephilim, of course, are extremely adept at using Vita, and it is unheard of for any Nephilim to not have any access to it.
Click here for a more detailed mechanical explanation of Vita.