Keyboard note charts help piano students learn which notes correspond with each key on the keyboard. The simplest keyboard charts only list the notes for the large white keys while full charts list also include sharp and flat notes on both the black and white keys.
Large key charts help student line up the keys with the 38 notes on sheet-music grand staffs that most written music uses. However, keyboards use repeating patterns of eight white keys and five black keys, creating one octave each. A one octave chart, containing both natural notes, along with sharps and flats, provides enough information to figure out the corresponding note for every key. Some charts also offer onomatopoeic methods for learning keyboard notes, such as assigning each key an animal with the same first letter as the key's note.
Keys on a keyboard are not notes per say. Piano keys correspond with a number of notes, as it would be impossible to create keys for every small subdivision of sharps and flats, as well as being unnecessary. For instance, even the central starting key on every keyboard, middle C, also corresponds with B sharp.
When first learning piano, students generally learn to play the middle octave of natural notes in the key of C, which are all white keys. After learning these, they add in the black keys for more complicated music with sharps and flats.