Session & Appl  r parts of State Management ...

 if v session one object in one form v can use it in all 
forms untill the project stop's.....

but,
 In Appl state if v store value it may use throughout 
applacation even stop and restart it so it is very useful 
for permanent data...

EX:In Some website they ll display the visitors no by 
incrementing Application State data by One each time a 
application Restarts.......

session object is used to store information between http 
request for a particular user. Application are globally 
across users.

application :Global User
Session :Single User

application state is a state where we hav the information
that is global for the application,
where as
session state is a state which is maintained as a 
per-client basis.
whenever a user first accesses a page a session id is
generated by asp.net.
that session id is then transmitted between the client and
the server via Http either  with the help of client-side
cookies or encoded in a mangled sessions of  the urls.
so the next time the users accesses,state associated with
that session id can be viewed or modified.

Both Application and session state are used to store the 
data when the postback occurs in the web form.

Session State – Session State information is available to 
all pages opened by a user during a single visit. 

Application State - Application State information is 
available to all pages, regardless of which user requests a 
page.