The second section in the Triggers tab is the Synchronisation palette. Opus can automatically have an action (or a series of actions) happen:
when a page or object appears (i.e. On Show trigger) or disappears (i.e. On Hide trigger) from the screen.
before a page or object appears (i.e. Pre-Show trigger) or disappears (i.e. Pre-Hide trigger) from the screen. Note that these triggers are not recommended for Flash publications.
when synchronised with the start or end of another event (i.e. the Synchronise triggers).
Synchronise to Animation Start Trigger
Synchronise to Animation End Trigger