Notifications are brief messages that users can access at any time from the status bar. They provide updates, reminders, or information that’s important, but not critical enough to warrant interrupting the user. Open the notifications drawer by swiping down on the status bar. Touching a notification opens the associated app. More on Notifications
Most notifications have a one-line title and a one-line message. The recommended layout for a notification includes two lines. If necessary, you can add a third line. Timestamps are optional.Swiping a notification right or left removes it from the notification drawer.
Android Design 