Very basic barrel roll: pitch up slightly, hold the small elevator input and add ailerons to roll the model. The plane will then corkscrew around, kind of like flying around the inside of the barrel, where you enter one end and fly out the other. The model will not exit on the same heading as the entry.

If you've ever seen the Blue Angels or Thunderbirds do their formation rolls, you'll see that they are all nicely-performed barrel rolls.