Can you please explain me the light reaction or 'Calvin Benson Cycle',PLZ..!

One correction - Light reaction is not called Calvin cycle. The light independent reaction, also called the dark reaction is the Calvin Benson cycle.

The process of photosynthesis takes place in 2 stages:

i) Light phase or reaction      and 

ii) Dark  phase or reaction  

 

Light reaction is the first stage of photosynthesis. It is an energy trapping and photochemical reaction which takes place in the grana of chloroplasts and in presence of light. It results in the formation of ATP and NADPH2. During this reaction, chlorophyll-a absorbs light energy and gets excited, thereby releasing an energy rich electron, leaving it ionised. This electron passes through a series of electron acceptors and ATP is formed in the process. There are 2 pathways of electron transfer called cyclic electron transfer and non-cyclic electron transfer.