The Present Perfect Tense:
The present perfect, like the other perfect
tenses (future and past perfects), conveys
the idea that one thing happens before
another time or event. In other words,
perfect tenses are always used within
a context and not in isolation.
To form the present perfect, use a form
of have + past participle:
--They've already dried their clothes.
--I've just finished washing my clothes.
--She's borrowed some detergent.
(In the above, the actions all took place
before now. The exact time is unimportant.)