Hi! The written form is را but a lot of people pronounce it as رو when they are talking to friends. Sometimes they don't say ر at all, and just say و. By the way, this is true in Iran. However, the dialects in Afghanistan and Tajikistan (Dari and Tajik) are more conservative, and the pronounciation is more similar to the written form, so I think را is more normal there (but I could be wrong!)

Are you asking about Farsi language? If yes, I can help. I am a native Farsi speaker. Ask your question clearly. You question is a bit confusing.

The question I was asking is the sometimes in Farsi, I read things like for example کتاب رو to refer to "the" book (definite), instead of یک کتاب = "a" book (indefinite). But sometimes I also see را to refer to "the" something just as رو. Is there a difference in usage?

As you may know we have 2 versions of Persian : official, colloquial. In colloquial Persian in many cases ا changes to و. For instance تهرانی»» تهرونی را»»رو همان»» همون حرام»»حروم And etc