Hi Manish,
Reflection and introspection refer to the same concept, of looking up a Class programmatically and inspecting the class like how many methods does it have, what are the super classes, implemented interfaces etc....in short you can actually "read" a class.
Not only that, you can also use this concept successfully to create Applications etc.
a good place to start is here
(Reflection Tutorial) A lot of Frameworks depends on reflection like
Struts etc, and soon you will appreciate the many ways you can use reflection.