how to retrive the app setting values in C3

If Settings are User Settings Then
Declare your settings file.

private static Properties.Settings settings;

//then in you main program

public frmMain()
        {
            InitializeComponent();
            settings = new Properties.Settings();
            settings.Reload();
        }

then in you calling method like
string getBaudRate()
{
return settings.BaudRate;
}

and if its app.config File Settings then
ConfigurationSettings.AppSettings["RetryCount"].toString();