Buttons express what action will occur when the user clicks or touches it. Buttons are used primarily to initialize an action, either in the background or foreground of an experience. Buttons differ from links in this regard, because links should only navigate the user to a new state in the application but never initialize any actions.
Usage & Behavior
If it is disabled, the cursor will indicate that the selection cannot be made.
Content Guidelines
Buttons are used primarily on action items. Some examples include Add, Save, Delete, Sign up. Do not use Buttons as navigational elements. Instead, use Links because it takes the user to a new page and is not associated with an action. Each page may have one to two primary buttons. Any remaining calls-to-action are represented as secondary buttons.
Labels
Button labels tell users what will happen when they click the button. Use verbs that describe the action, such as Add or Delete. Use sentence-style capitalization (only the first word in a phrase and any proper nouns capitalized) and no more than three words for button labels.
For Sets of Buttons, use specific labels, such as Save or Discard, instead of using OK and Cancel. This is particularly helpful when the user is confirming an action.