it's - it is
but the contraction can also be : it has
we know which, because 'been' follows it, to make the present perfect tense:
1) It has been raining outside. 2) It has been a great pleasure to be here.
Can you clarify me, as to how these two above mentioned sentences are different from
Notice that it is present tense
1) It is raining outside -
2) It is a great pleasure to be here.