Your notifications can be found in the menu on the left. Here, you'll get all sorts of alerts.
To complete the action associated with each notification, simply click on the blue button within the notification. For example:
You can customize the kinds of notifications you receive, as well as how you receive them. To do so, go to Settings and then the Notifications tab. Here, the types of notifications are organized into dropdown menu categories. You can turn any notification off by clicking on the switch to the right of the notification type. Note that, depending on the type of notification, you have the option of being notified by email and/or push notification.