Notifications

Open Notifications from the bottom bar of the menu; its number is how many you have not seen. New ones show first (New), the older ones under Earlier.

NotificationWhat you can do
ExampleUser invited you to join a worldJoin or Decline, while the invite lasts (5 minutes): it shows the minutes left, then expired.
ExampleUser sent you a friend requestAccept or Decline.
ExampleUser accepted your friend requestNothing to do: you are friends.
A world is not served on your serverFor the owner and the co-owners of a server: why the server does not serve this world, and what to do (see Each world is checked).

On top, Site requests: a world that wants to contact a site and waits for your answer, with Deny, This time and Always and no cross. It stays until you answer or leave the world. See Sites a world contacts.

Each notification has its cross to remove it; Clear all removes them all. Which notifications you get is in Settings, Notifications. The same notifications are on the website (see Notifications on the website).

While the menu is closed

An invite, an invite request for your instance, and a world's question about a site come into view as a window, so you do not miss them. In VR it floats a little below your eyes and follows your head; with keyboard and mouse it is in the top right corner of the screen (Tab shows the pointer to click it).

WindowButtons
ExampleUser invited you to join a worldDecline or Join, while the invite lasts.
ExampleUser asks for an invite to a worldDeny or Approve.
ExampleWorld wants to contact example.comDeny, This time or Always (see Sites a world contacts).
ExampleUser sent you a message, with the start of the messageNone: it goes by itself after a few seconds. The message stays in Messages.
ExampleUser joined the instance, ExampleUser left the instanceNone: it goes by itself after a few seconds.

The cross only closes the window: the invite stays in Notifications, the invite request on the World page.