after going through lots of chaos..it is almost clear to me..just one small doubt..where i got stuck...
which is this tense which represent

CONDITIONNEL + PARTICIPE PASSE

e.g.
i would have known
j'aurais su


i would have gone
Je serais allé


i would have told
J'aurais dit

is the translation right ???
which tense exactly???


thanks in advance

Correct, "conditionnel passé" ("conditional perfect" in English)

Tom

well i understand it now better.

use verb être or avoir in conditionnel (aurais/serais)+ participe passe = passe conditionnel

either to use verb etre or avoir depends on the second verb, same as in case with passe compose

i would have known/ j'aurais su (with avoir)
&
i would have gone/ je serais allé (with être as verb aller uses être )


i would is "conditionnel"
and
i would have is "conditionnel passe"

ok..
here comes another doubt..

which tense do u use to express has been / have been in french ???

It depends the context. It can be present, passé composé or a periphrase.


I've been ill the whole week = je suis malade depuis une semaine - j'ai été malade toute le semaine - ça fait une semaine que je suis malade

They've never been in Switzerland = ils ne sont jamais venus/allés en Suisse

We've been married for 5 years = nous sommes mariés depuis 5 ans

If there is something else after has been, like has been doing, then it's even more depeding on context, but present tense seems probable if the said action is still going on or the point still valid.

yes i got it now..
has been/ have been are simply translated as

1. PRESENT (if the work is still going on)

i have been studying french for two years - j’étudie le français depuis deux ans. (and she is still studying)


2. PASSE COMPOSE (if the work has already finished)

i have been studying lately - j'ai étudié récemment (as she is no longer studying)

Sounds good for a chort version and the two sentenses are correct. But what is considered achieved is sometimes difficult to find out. Adverb "lately" gives it away here, you're right. .