[Koha] Koha for beginners

[Mehvish Farah]

Hi,
I am new to Koha and have no library science experience.
I am trying to understand MARC but stuck at the terms where there are some
numbers with a dollar sign and then an alphabet. What is this basically?
I would be grateful if someone can help me with a book or link that helps
understand these terms or library/koha terms in general or in easy
comprehension.

other thing that i want to know is if a book is bilingual (Spanish and
English or Arabic and English) , what should i write in Lnaguage code clumn?

Thanks
*Mehvish*