Activate Llanowar Scout by tapping it, putting Azorius Chancery from your hand onto the battlefield.
When Azorius Chancery enters the battlefield, it and Elven Raft-Steerer trigger.
Resolve the Azorius Chancery trigger, returning itself from the battlefield to your hand.
Resolve the Elven Raft-Steerer trigger, untapping Llanowar Scout.
Repeat.
This clever little loop uses Llanowar Scout's tap ability to continually drop Azorius Chancery straight into play from your hand. Because Azorius Chancery has a mandatory enters-the-battlefield trigger that bounces itself back to your hand, you naturally generate a fresh land drop on command. Meanwhile, Elven Raft-Steerer sits on the board watching all this land-based activity, triggering off the new arrival to untap Llanowar Scout and leave it ready to do it all over again.