Notifications are alerts sent to the user when another user sends them a message, adds a comment, or likes a photo or video posted by that user.
To block another user simply click the settings icon found on each profile and choose block member. You can block someone to prevent them from seeing things that is posted on your profile, starting conversations with you or adding you as a friend. Blocking someone you are friends with will automatically unfriend them.
This feature is not available in the chat room.