I looked on the wiki and it says its extracted from a snake head. Unfortunately, i dont know how to extract stuff, and ive looked everywhere for it. Can someone help me out?
The snake heads are a resource drop from the snakes themselves. The buff "resource finder" is a great help in getting them to drop if your having trouble getting them. You can find two different potions with that buff under special items in the auction house (AH for short). Players can buff you with it as well.
From there, you can find the heads in your backpack. Clicking them will extract them, right clicking will give you the option to extract all you have. The buff "extractor" will increase the chance of success in getting a resource from it, while "extractor 2" gives a chance to save the resource when extracting it. Both of these can be found in the buff market, or from higher level guild members if you can
If ever you need to find a specific resource for a potion in the future, while the ultimate fallensword guide (usfg) is helpful, I would still recommend the wiki (even in it's dilapitated state), both of which can be found under resources on the left side of the screen.
Hopefully this was helpful and informative.