MSDN is an acronym for Microsoft Developer network. For those new to Visual Studio / and Microsoft development think of it as an insurance premium. As insurance it protects, in this case from software version changes, but it is much more than this as it offers a stream of invaluable services. Some of which are listed in the links shown below.
MSDN Subscriptions – Learn what an MSDN Subscription offers you and take advantage of the Microsoft software and services.
MSDN Subscription Benefits – Learn about all the benefits and savings.
MSDN Golden Rules – Read the important things to know and understand.