The Dvorak keyboard is an alternative way of putting letters on an English keyboard. Most English keyboards have the keys lined up in a "QWERTY layout." The point of QWERTY was to prevent typewriter keys from sticking, but it is not the most "ergonomic", or comfortable, keyboard to type on. Augustine Dvorak invented the Dvorak keyboard, where letters are arranged based on how often they are used. For instance, the most common letters (like "e") are in the center row of keys, so less hand movement is needed when a person is typing.
Now that we use computers instead of typewriters, there is no reason to keep the QWERTY keyboard, except that everyone already learned to type using it. Many Dvorak keyboard users think that more people should use the Dvorak keyboard, as it aims to prevent typing injuries (like Repetitive Stress Injury and carpal tunnel). But most users are used to the QWERTY keyboard, and do not want to switch.