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.