Overture and beginners!

• Overture: A piece of orchestral music containing contrasting sections, played at the beginning of an opera, oratorio, or play.

• Beginners: Actors who appear in the first scene of a play

• "Overture and beginners!": In the theater, a call boy's spoken cue for the orchestra to begin playing the overture and the actors in the first scene to get into position. So here, "Shaun is about to give a speech, get ready to hear something important (pompous and overblown)"