I have created a C# console based project. In that project i have some variables like companyName, companyType which are Strings.
Right click on the project file -> Add -> New Item -> Application Configuration File. This will add an app.config (or web.config) file to your project.
The ConfigurationManager class would be a good start. You can use it to read different configuration values from the configuration file.
I suggest you start reading the MSDN document about Configuration Files.
Configuration configManager = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
KeyValueConfigurationCollection confCollection = configManager.AppSettings.Settings;
confCollection["YourKey"].Value = "YourNewKey";
configManager.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection(configManager.AppSettings.SectionInformation.Name);
Add an Application Configuration File item to your project (Right -Click Project > Add item). This will create a file called app.config in your project.
Edit the file by adding entries like <add key="keyname" value="someValue" /> within the <appSettings> tag.
Add a reference to the System.Configuration dll, and reference the items in the config using code like ConfigurationManager.AppSettings["keyname"].