tense

1. I have purchased one notebook. 現在分詞式: 我剛剛買了一本筆記簿.
2. I purchased one notebook. 過去式: 我已買了一本筆記簿.

I have purchased one notebook.

這句係past perfect
代表此動作對現在有影
e.g. I've lost my keys, so I can't open the door.
唔見左keys, 令你現在開唔倒門

I purchased one notebook

這句純粹係past tense
講番過去做左咩

***全篇由自己打, 無copy & paste

2008-04-12 22:41:02 補充：
第一句係present perfect, 唔係past perfect
sorry

past perfect 係用"had",唔係 "have".