I was honoured to be chosen to represent my school at the national debate competition.

represent 是动词，由前缀 re-（表示"再次"或"回"）和词根 present（呈现、展示）组成，字面意思是"再次呈现"或"代为展示"。在这里表示"代表"某人或某机构出席或发言。