Where the Notes Fall on a Keyboard

On a keyboard, the white keys are the "natural" notes, and the black keys are the "sharp" and "flat" notes. Naturals, sharps and flats are discussed further in Key Signatures.

Middle C, discussed in Notes on Staves, is a natural (white) key, and is approximately the center key of a piano, which has 88 keys. Some keyboards and organs have less than 88 keys, but the same basic rule applies.

As you'll notice (especially if you're looking at a keyboard), not all notes have sharps or flats (there's no C or F flat, nor is there B or E sharp).