Sam will be training for his role: Active - Sam will be training, possibly without anybody's help. Train is used intransitively here, with a progressive form of the verb.
Sam will be trained by a coach for his role: Passive - the coach will train Sam. Train is used transitively here, with a non-progressive form of the verb.
Sam will be being trained by a coach for his role: Passive and progressive. The coach will be training Sam. Train is used transitively.
Student or Learner