Connection string, Web.config, App settings..

i will try to explain in layman terms :)

postback is any action which causes refresh by any action like a button click or dropdown selection changed or check box changed or any event

ispostback is a boolean property which is set to true if page is a postback

without web.config we cannot run the app

web.config is the config file where all the configurations like connection string or handlers or service configuration anything can be set

connectiong string can be set in page_load. it is advicable to write connection string in web.config so that it will be easy for you to change any future database server changes in config file than changing in code level.

 The element stores custom application configuration information such as database connection strings, file paths, XML Web service URLs, or any information stored in an application's .ini file. The key/value pairs specified in the element can be accessed in code using the System.Configuration.ConfigurationSettings class.

Diff is App settings is an element in web.config and web.config is a configuration file