[Yogesh]

How to understand the organic chemistry reactions very well

[Babcock_Hall]

That is a very large and very open question.  Two things come to mind.  One is to write down reactions; don't just look at them.  Two is to look for types of chemistry, such as oxidation or reduction, so that one can better understand them.

[kriggy]

Well everyone has a system or method but basicaly:

a) try to understand the concepts behind - electrophility, nucleophility etc..
b) although there is some memorization involved, try not to memorize all reactions but understand the mechanism behind it so you can apply it on different molecules. I had some succes using R´s instead of specific alkyl chains so I would realize that it can work on many similar compounds not just on the one in book
c) practice, practice practice
d) And in the end, you will realize that doing the chemistry in lab is totaly diffent that writing it on piece of paper