How do I do a Barrel Roll?
If you look at the screen, you will notice it'll give you a hint on how to perform the barrel roll in the text blurb.
You can perform a barrel roll by pressing Z or R twice
Here is a video showing the blurb and a successful barrel roll.
If I recall correctly, double tap the R or Z keys on top of the controller. Its when your craft spins left or right. Great for avoiding incoming enemy's or projectiles.
(Z or R twice)!!