The postcard served him as a bookmarker.是什么意思？

The postcard served him as a bookmarker.

这张明信片作了他的书签.

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

postcard

n. 明信片；

例句
The army sent me a postcard acknowledging my request.
军队寄给我一张明信片告知我的申请书已收到。

served

vt.& vi. serve的过去式；v. （为…）服务( serve的过去式和过去分词 )，任（职），提供，端上；

例句
The American served three aces in the opening game of the set.
这位美国选手在该盘首局有三次发球直得。

him

pron. (he的宾格)他；

例句
They said goodbye to him as he got aboard the train at Union Station.
当他在联合火车站登上火车之际，他们向他道别。

as

adv. 同样地，一样地，例如；prep. 作为，以…的身份，如

例句
As far as I can recall, Patti was a Smith.
我记得帕蒂是姓史密斯的。

bookmarker

n. 书签；

例句
Put a bookmarker into the book so that I can konw where you have read.
书里面放上书签,我好知道你读到哪儿了.