Explain bible structure to a muslim

Im a muslim. so the structure of our book and its organisation is different.

we have chapters and verses. all in a single book. we beleive is directly the word of god, not devinely inspired.

now for the bible i understand it has chapters and verses too but in multiple books.

now some questions (plz answer theses first then explain more if you want):

old testemant and the new one? what are they whats the difference? is old the torah and new the bible?

explain versions of same book? is it translations or what?

can old be followed? what is need to change?

what does it mean the people who wrote where devinely inspired, god took control of body or were they guided?

does being devinely inspired mean its subject to human error?

do all christians beleive in the same books?

when in bible it is spoken in first person, who is speaking, god or the writer?

why are there inconsistensies between different and even the same bible? which is taken as correct?

why do some verse contain footnotes saying it wasnt there in ancient greek manuscripts? and why where they added? (cant explain my question cuz i genuianly dont understand so i will expand on this one)

https://www.biblegateway.com/passage/?search=1+John+5%3A7-8&version=NIV

https://www.biblegateway.com/passage/?search=1+John+5%3A7-8&version=KJV

NIV contains footnotes that from what i understand says that the extra part in KJV is an addition, so why is the KJV still considered a bible if it has added verses with no proof behind them. so one more question is why older less acurate versions are considered bible.