want to know the use of 之 ? Is there a specif - Cchatty

Basically it's like the possesive 'apostrophe s' in English.
苏轼之友 Su Shi's friend(s)
But it's very literate this way.

Then we also use 之 like this:
这些书之一/二/... it's still possesive, but in English we use 'of' for cirsumstances like this
one/two/... of these books

this has many meanings, but most common one is that it is the same as 最 or "one of" but always put it at the end.
for exemple: 他是我朋友之一.