Peanut butter is made from ground up peanuts and salt. This is all that is necessary (even the salt isn't mandatory, but the flavor is better).

Commercial peanut butter also often add sugars, hydrogenated vegetable oils (e.g. cottonseed, soybean, rapeseed), preservatives, etc.

Without the hydrogenated vegetable oils added the peanut oil rises to the top and you have to keep mixing it back in before using the peanut butter. A few brands of commercial peanut butter offer "old fashioned" peanut butter without these oils added (but they may still add the other things).