yet作副词意为“用于否定句和疑问句，谈论尚未发生但可能发生的事；现在；即刻”，作连词意为“但是；然而”。already副词意思是“早已；（表示惊奇）已经，都；（强调情况或问题存在）已经”。already多用于肯定句，而yet多用于疑问句和否定句。
yet的用法
（1）Have you seen that film yet?
你看过那个电影吗？
（2）Has Tim done his homework yet?
蒂姆做完作业了吗？
（3）She hasn't finished the report yet.
她没有完成报告。
（4）Doug and Tom haven't telephoned yet.
道格和汤姆没有通电话。
already的用法
（1）She had already eaten when he arrived.
当他到达时，她已经吃完了。
（2）Jackson had already done his homework when he was asked for help.
当他求助时，杰克逊已经完成作业了。
（3）The guests have already arrived.
客人已经到了。