app.config

App.config how to use encrypted ConnectionString

In my app.config I have a section that for my String connection: </configSections> <connectionStrings> < ... , where he suggested to use the index 0, he passes, but this bringing a String totally different from the original String:

What is AppSettings for?

I was taking a look at the Web.confg and would like to know what the <appSettings> is for? What does it interfere with our application?