"For example" and "for instance" are often used interchangeably, but do have some nuance between them. "For example" is broader, indicating a description of a class or category being described. "For instance" is narrower in scope, referring to a specific instance in the large class described by the example. Additionally, "for example" would be appropriate to use when creating a hypothetical, but "for instance" should always refer to something real - a concrete member of a class or category or an exemplary event which has occurred.