They reported what they had seen.是什么意思？

They reported what they had seen.

他们把看到的情况作了举报。

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

reported

adj. 据报告的，据报导的，据传闻的；

例句
A Dr Matthew Owens was reported missing while on an expedition to north-eastern Turkey.
据报道，一位叫马修·欧文斯的博士在前往土耳其东北部考察的途中失踪了。

what

pron. （用以询问某人或某事物的词）什么，多少，…的事物；adj. …的（事物或人）；adv. （用于感叹句中）；int. （用以表示不相信或惊奇），（用以表示未听清楚对方说的话）；

例句
How big is the abyss between what you think you are and what you actually are?
你对自己的认识和真实的你之间差别到底有多大？

had

v. 有（ have的过去式和过去分词 ），（亲属关系中）接受，拿，买到；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

seen

v. 看见( see的过去分词 )，观看，领会，考虑；

例句
Holiday spots have seen a dramatic revival and tourist chiefs are competing for a slice of the action.
各个度假点重又呈现出一派兴旺景象，旅游业的龙头老大们都在争着分一杯羹。