talking about recent past " some thing happened few seconds ago " is one of the uses of present perfect ? For example : I'm walking with my friend " Ooh, I have dropped my pen, can you help me to find it ? " ... is that right ? If it's right so, present perfect the only tense can be used to talk about very recent actions or past simple aslo ?
The word just can be used in the Present Perfect tense to speak about something that happened a short time ago:
- I have just dropped my pen. Can you help me find it?
"Just" is mostly used in the Present Perfect and comes between the auxiliary verb (have) and the past participle.
Another possible way to say it is to use the set phrase "just now" which means only a moment ago; a little time ago; at this moment.
- I (have) dropped the pen just now. Can you help me find it?
You can use past tense or present perfect tense when referring to events that happened, regardless of how recent the action you're referring to was. Often you'll prepend the word just to indicate that you're talking about an event that happened in the recent past. For instance, if you wanted to talk about an event where a car drove past you a few seconds ago, you could say something like:
That car just drove past me!
You use the past tense drove as you are referring to an event in the past, and you use just to indicate the event happened very recently.
Regarding present perfect, I would defer to SovereignSun's answer; it explains the concept more concisely than I could manage.
With regards to your example, the correct ways to phrase it are:
...can you help me find it?
..can you help me with finding it?
English simply does not have syntax or morphological markers to indicate differing degrees of recency.
If you said, "I have eaten lunch", the listener could reason that you mean that you have eaten lunch recently, simply because every human being on Earth has eaten lunch at some point in his live, and you have no reason to make an inherently obvious statement like "I have eaten lunch at least once in the last 20 years."
If you said, "I have eaten dog meat", then the listener could reason that you have done it but not necessarily recently -- indeed probably not recently, because eating dog meat is (in most English-speaking countries) an unusual event, so if it were recent, you would have said, "I ate dog meat just now!"
A transitory and temporary state like pen-less-ness falls into the first category, but only for semantic reasons, not syntactic ones.