Basic areobatic maneuver, used to shake an enemy from your tail. You corkscrew in the sky and lose airspeed, and your enemy flies right by you.
To perform a barrel roll, bank sharply left or right, and gently pull back on the stick to maintain the roll. Hold sideways pressure on the stick as you roll inverted, then center it when you return to level flight.
During this move, the stick is essentially in the Left or right rear corner of the cockpit. The nose will draw a circle on the horlizon, instaed of rotating on a point. If you do a barrel roll perfectly, you won't lose any altitude
These people who say to perform a barrel roll by pushing buttons don't know how to fly worth shit and I would own them in any aerial combat game.