Van and von are surname prefixes that are found in European surnames; there are also other prefixes in other European languages, and countries like the French have prefixes like De, La, Le, Des, and Du. The Portuguese have prefixes like Da and Dos.
The Spanish have prefixes like Las, De, las, Del. and other European countries have prefixes too. Some people's surname was adopted from a different point of reference, which identifies them from others, from a person's father or ancestors, profession, physical characteristics, place of origin, etc.
Van and von are prefixed surname, which means from and for. Von is the German origin used by members of noble families in the middle ages after the middle age is have to be transformed to the common prefix in German that it is even used by commoners.
Van is Dutch in origin; it is used by common folks, and also it indicates a geographical location, and van is attached to the surname itself. The van can come in other forms, too, like Van der.