What is spin spin coupling? I am studying nmr and the concept of multiplicity is very hard to undersand. Specifically I wanted to know where this arises form. Can anyone explain the concept of spin spin coupling in detailed and in simple terms?
As it stands, your question is very general. It is unlikely that a single answer here will describe spin coupling and multiplicity in a simple and detailed manner any better than any publicly available reference source. There are hundreds available. I suggest you read one or more of the following extremely useful introductory NMR references, and ask more specific questions that you do not understand from them.


Reich (http://www.chem.wisc.edu/areas/reich/chem605/)
Hornak (http://www.cis.rit.edu/htbooks/nmr/) 
Libretexts (https://chem.libretexts.org/Core/Organic_Chemistry/Spectroscopy/Nuclear_Magnetic_Resonance_Spectroscopy
and
https://chem.libretexts.org/LibreTexts/Purdue/Purdue%3A_Chem_26200%3A_Organic_Chemistry_II_(Wenthold)/Chapter_12._Nuclear_Magnetic_Resonance)