The advertisement said that Danny Brook was one of the starring actors but he was replaced by another extremely disappointing and inexperienced actor.

inexperienced 是由前缀 in-（表示"否定"）和形容词 experienced（有经验的）组成的复合词。experienced 来自名词 experience（经验）加后缀 -ed 构成形容词。因此 inexperienced 字面意思是"没有经验的"，指缺乏相关技能或知识的状态。