You really should be using the built in Application Settings
You can directly access simple settings using the ConfigurationManager
ConfigurationManager.AppSettings["MySetting"] = "SomeStuff";
var mySetting = ConfigurationManager.AppSettings["MySetting"];
There is also direct access to your Connection Strings using the ConfigurationManager
var conn = ConfigurationManager.ConnectionStrings["DevSqlServer"];
All this is stored in XML files, and by default your *.config files.
To Answer Doomsknight's question from the comments
Configuration settings can be done a number of ways, but by default, they are stored in two places.
Application Level Settings are stored in a configuration file.
For executable programs this file is located in the same directory as the .exe and is named after the assembly, or executable.
Example: MyAssembly.config
, Another.Assembly.config
For web applications, the settings are stored in the web.config file (usually) located in the root directory of the web application. These are applied hierarchically and one can be located at each directory level of the Web Application.
Example: MySite\web.config
, MySite\SubDirectory\web.config
User Scoped Settings are stored in the user profile
Example: C:\Documents and Settings\USERNAME\Local Settings\Application Data\ApplicationName
Connection Strings are stored in the <connectionStrings></connectionStrings>
section in your config file.
<connectionStrings>
<clear />
<add name="Name"
providerName="System.Data.ProviderName"
connectionString="Valid Connection String;" />
</connectionStrings>
These settings can easily be modified directly in the config file, but without writing some code to automatically refresh sections of the config file (which is possible), an application restart is typically needed.
I hope this helps out.