The means you need to do something — most often the money, but it can also be the skill, energy, courage, or resources. "He doesn't have the wherewithal to start a business" usually means he lacks the money; "she lacked the emotional wherewithal to face them" means she lacked the inner strength. It is a noun, always singular, and it almost always comes with "the" and then "to do something": have / lack / find the wherewithal to do X. It sounds formal but slightly warm, the kind of word you see in newspapers and hear from older, well-read speakers rather than in casual chat. There is a nice flexibility here that dictionaries often flatten: the word does not name the resource, it names having-enough-of-whatever-it-takes, so the reader fills in the right kind from the situation. Long ago it was an adverb meaning simply "with which"; the noun we use now only appeared around 1800.