See the recipe here: http://herb.co/recipes/quick-easy-cannabutter/
See why you need to decarboxylate your weed and why here: http://herb.co/decarboxylation/
“In order to release the full potential of marijuana’s psychoactive effects, you must first go through a process called decarboxylation. It is highly recommended you do this before you begin cooking with cannabis.
Raw cannabis contains a lot of THCA, which is not psychoactive (meaning it doesn’t get you high). However when you apply heat, such as a flame or vaporize, cannabis becomes ‘decarboxylated’ by the heat and at this point becomes psychoactive (gets you high).
So, if you ingest cannabis and want the full psychoactive effect, you need to first decarboxylate before cooking with cannabis.”