In this scene, Jonas accidentally transmits a memory to Gabe. The memory was of a calm ocean with a sail.
This is about Jonas' realization that when someone was 'released', they were actually being murdered. The Giver shows him this by means of playing the security footage from that morning's release of a twin baby directed by Jonas' father, himself. This scene also mentions the process of choosing the baby that weighs less and 'releasing' that one.
He killed it! My father killed it!
Towards the end of the book, Jonas escapes and takes Gabe on his father's stolen bicycle. It is mentioned that Gabriel would warn Jonas if any plane was heard or seen close to them by saying "Plane! Plane!" as shown above.